Verify that books are correctly rebuilt when attribute files change

When #1888 and #1887 were merged, the resulting [build](https://elasticsearch-ci.elastic.co/job/elastic+docs+master+build/2999/console) didn't rebuild all the correct books. It seems like the actual changes in https://github.com/elastic/built-docs/commit/4860e71b2fd1fd7384129b895d355ab4c9237f68 were because of [this contemporaneous change](https://github.com/elastic/elasticsearch/commit/f3323b9e55b0198fb882ac151de3b82597aa392c) in the ES docs.

Full Build Log

```
Started by user James Rodewig
Running as SYSTEM
[EnvInject] - Loading node environment variables.
Building remotely on elasticsearch-ci-immutable-docs-1595855024854168217 (immutable docs swarm) in workspace /var/lib/jenkins/workspace/elastic+docs+master+build
using credential f6c7695a-671e-4f4f-a331-acdce44ff9ba
Wiping out workspace first.
Cloning the remote Git repository
Cloning repository https://github.com/elastic/docs.git
> git init /var/lib/jenkins/workspace/elastic+docs+master+build # timeout=20
Using reference repository: /var/lib/jenkins/.git-references/docs.git
Fetching upstream changes from https://github.com/elastic/docs.git
> git --version # timeout=20
using GIT_SSH to set credentials GitHub user @elasticmachine SSH key
> git fetch --tags --progress https://github.com/elastic/docs.git +refs/heads/*:refs/remotes/origin/* # timeout=20
> git config remote.origin.url https://github.com/elastic/docs.git # timeout=20
> git config --add remote.origin.fetch +refs/heads/*:refs/remotes/origin/* # timeout=20
> git config remote.origin.url https://github.com/elastic/docs.git # timeout=20
Fetching upstream changes from https://github.com/elastic/docs.git
using GIT_SSH to set credentials GitHub user @elasticmachine SSH key
> git fetch --tags --progress https://github.com/elastic/docs.git +refs/heads/*:refs/remotes/origin/* # timeout=20
> git rev-parse refs/remotes/origin/master^{commit} # timeout=20
> git rev-parse refs/remotes/origin/refs/heads/master^{commit} # timeout=20
Checking out Revision 9ed7032131362962436e26ba2e115b2b168baf92 (refs/remotes/origin/master)
> git config core.sparsecheckout # timeout=20
> git checkout -f 9ed7032131362962436e26ba2e115b2b168baf92 # timeout=20
Commit message: "Updates 6.8 version attributes (#1887)"
> git rev-list --no-walk e2c7904bb9a2b5167290da51b57666c6c1673922 # timeout=20
[EnvInject] - Mask passwords that will be passed as build parameters.
[elastic+docs+master+build] $ /usr/local/bin/runbld /tmp/jenkins7149818731521058195.sh
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF8
runbld>>> runbld started
runbld>>> 1.6.12/f45d832f2ba0aa2722ab4ec1fda8ad140f027f8b
runbld>>> The following profiles matched the job 'elastic+docs+master+build' in order of occurrence in the config (last value wins).
runbld>>> Matches in the system config:
runbld>>> - Matched ^elastic\+docs
runbld>>> Debug logging disabled.
runbld>>> Storing result
runbld>>> Store result: created {:total 2, :successful 2, :failed 0} 1
runbld>>> BUILD: https://c150076387b5421f9154dfbf536e5c60.us-west1.gcp.cloud.es.io:9243/local-test-build-1531848254847/t/20200727130552-2EC64D96
runbld>>> Adding system facts.
runbld>>> Adding vcs info for the latest commit: 9ed7032131362962436e26ba2e115b2b168baf92
runbld>>> >>>>>>>>>>>> SCRIPT EXECUTION BEGIN >>>>>>>>>>>>
runbld>>> Adding /usr/lib/jvm/java-8-openjdk-amd64/bin to the path.
+ set -eo pipefail
+ export HOME=/var/lib/jenkins
+ HOME=/var/lib/jenkins
+ export 'GIT_AUTHOR_NAME=Jenkins CI'
+ GIT_AUTHOR_NAME='Jenkins CI'
+ export GIT_AUTHOR_EMAIL=jenkins@elasticsearch-ci.elastic.co
+ GIT_AUTHOR_EMAIL=jenkins@elasticsearch-ci.elastic.co
+ export 'GIT_COMMITTER_NAME=Jenkins CI'
+ GIT_COMMITTER_NAME='Jenkins CI'
+ export GIT_COMMITTER_EMAIL=jenkins@elasticsearch-ci.elastic.co
+ GIT_COMMITTER_EMAIL=jenkins@elasticsearch-ci.elastic.co
+ '[' false == true ']'
+ '[' false == true ']'
+ ssh-agent bash -c '
ssh-add &&
./build_docs --all --push --target_repo=git@github.com:elastic/built-docs --reference=/var/lib/jenkins/.git-references '
Identity added: /var/lib/jenkins/.ssh/id_rsa (/var/lib/jenkins/.ssh/id_rsa)
INFO:build_docs:Updating repositories
INFO:build_docs: - target_repo: Cloning from
INFO:build_docs: - target_repo: Checking out minimal
INFO:build_docs: - target_repo: Checking out remaining
INFO:build_docs: - apm-agent-dotnet: Cloning from
INFO:build_docs: - apm-agent-go: Cloning from
INFO:build_docs: - apm-agent-java: Cloning from
INFO:build_docs: - apm-agent-nodejs: Cloning from
INFO:build_docs: - apm-agent-python: Cloning from
INFO:build_docs: - apm-agent-ruby: Cloning from
INFO:build_docs: - apm-agent-rum-js: Cloning from
INFO:build_docs: - apm-server: Cloning from
INFO:build_docs: - azure-marketplace: Cloning from
INFO:build_docs: - beats: Cloning from
INFO:build_docs: - clients-team: Cloning from
INFO:build_docs: - cloud: Cloning from
INFO:build_docs: - cloud-assets: Cloning from
INFO:build_docs: - cloud-on-k8s: Cloning from
INFO:build_docs: - curator: Cloning from
INFO:build_docs: - ecctl: Cloning from
INFO:build_docs: - ecs: Cloning from
INFO:build_docs: - eland-docs: Cloning from
INFO:build_docs: - elasticsearch: Cloning from
INFO:build_docs: - elasticsearch-hadoop: Cloning from
INFO:build_docs: - elasticsearch-js: Cloning from
INFO:build_docs: - elasticsearch-net: Cloning from
INFO:build_docs: - elasticsearch-perl: Cloning from
INFO:build_docs: - elasticsearch-php: Cloning from
INFO:build_docs: - elasticsearch-php-cn: Cloning from
INFO:build_docs: - elasticsearch-py: Cloning from
INFO:build_docs: - elasticsearch-rs: Cloning from
INFO:build_docs: - elasticsearch-ruby: Cloning from
INFO:build_docs: - enterprise-search-pubs: Cloning from
INFO:build_docs: - go-elasticsearch: Cloning from
INFO:build_docs: - guide: Cloning from
INFO:build_docs: - guide-cn: Cloning from
INFO:build_docs: - kibana: Cloning from
INFO:build_docs: - kibana-cn: Cloning from
INFO:build_docs: - logstash: Cloning from
INFO:build_docs: - logstash-docs: Cloning from
INFO:build_docs: - observability-docs: Cloning from
INFO:build_docs: - security-docs: Cloning from
INFO:build_docs: - sense: Cloning from
INFO:build_docs: - stack-docs: Cloning from
INFO:build_docs: - swiftype: Cloning from
INFO:build_docs: - x-pack: Cloning from
INFO:build_docs: - x-pack-elasticsearch: Cloning from
INFO:build_docs: - x-pack-kibana: Cloning from
INFO:build_docs: - x-pack-logstash: Cloning from
INFO:build_docs:Building docs
INFO:build_docs: - Installation and Upgrade Guide: Building 7.x...
INFO:build_docs: - Installation and Upgrade Guide: Finished 7.x
INFO:build_docs: - Installation and Upgrade Guide: Building 7.9...
INFO:build_docs: - Installation and Upgrade Guide: Finished 7.9
INFO:build_docs: - Installation and Upgrade Guide: Building 7.8...
INFO:build_docs: - Installation and Upgrade Guide: Finished 7.8
INFO:build_docs: - Installation and Upgrade Guide: Building 7.7...
INFO:build_docs: - Installation and Upgrade Guide: Finished 7.7
INFO:build_docs: - Installation and Upgrade Guide: Building 7.6...
INFO:build_docs: - Installation and Upgrade Guide: Finished 7.6
INFO:build_docs: - Machine Learning: Building 7.x...
INFO:build_docs: - Machine Learning: Building 7.9...
INFO:build_docs: - Machine Learning: Building 7.8...
INFO:build_docs: - Machine Learning: Finished 7.x
INFO:build_docs: - Machine Learning: Building 7.7...
INFO:build_docs: - Machine Learning: Finished 7.9
INFO:build_docs: - Machine Learning: Building 7.6...
INFO:build_docs: - Machine Learning: Finished 7.8
INFO:build_docs: - Machine Learning: Finished 7.7
INFO:build_docs: - Machine Learning: Finished 7.6
INFO:build_docs: - Elasticsearch Reference: Building 7.x...
INFO:build_docs: - Elasticsearch Reference: Building 7.9...
INFO:build_docs: - Elasticsearch Reference: Building 7.8...
INFO:build_docs: - Elasticsearch Reference: Finished 7.x
INFO:build_docs: - Elasticsearch Reference: Building 7.7...
INFO:build_docs: - Elasticsearch Reference: Finished 7.9
INFO:build_docs: - Elasticsearch Reference: Building 7.6...
INFO:build_docs: - Elasticsearch Reference: Finished 7.8
INFO:build_docs: - Elasticsearch Reference: Finished 7.7
INFO:build_docs: - Elasticsearch Reference: Finished 7.6
INFO:build_docs: - Elastic Cloud on Kubernetes: Building master...
INFO:build_docs: - Elastic Cloud on Kubernetes: Building 1.2...
INFO:build_docs: - Elastic Cloud on Kubernetes: Building 1.1...
INFO:build_docs: - Elastic Cloud on Kubernetes: Finished master
INFO:build_docs: - Elastic Cloud on Kubernetes: Finished 1.1
INFO:build_docs: - Elastic Cloud on Kubernetes: Finished 1.2
INFO:build_docs: - Elastic Cloud on Kubernetes: Building 1.0...
INFO:build_docs: - Elastic Cloud on Kubernetes: Building 1.0-beta...
INFO:build_docs: - Elastic Cloud on Kubernetes: Finished 1.0-beta
INFO:build_docs: - Elastic Cloud on Kubernetes: Finished 1.0
INFO:build_docs: - Filebeat Reference: Building 7.9...
INFO:build_docs: - Filebeat Reference: Finished 7.9
INFO:build_docs:Writing main TOC
INFO:build_docs:Compiling web resources
INFO:build_docs:Writing extra HTML redirects
INFO:build_docs:Writing nginx redirects
INFO:build_docs:Checking links
INFO:build_docs:Checking Kibana links
INFO:build_docs: Branch 5.0
INFO:build_docs: Branch 5.1
INFO:build_docs: Branch 5.2
INFO:build_docs: Branch 5.3
INFO:build_docs: Branch 5.4
INFO:build_docs: Branch 5.5
INFO:build_docs: Branch 5.6
INFO:build_docs: Branch 6.0
INFO:build_docs: Branch 6.1
INFO:build_docs: Branch 6.2
INFO:build_docs: Branch 6.3
INFO:build_docs: Branch 6.4
INFO:build_docs: Branch 6.5
INFO:build_docs: Branch 6.6
INFO:build_docs: Branch 6.7
INFO:build_docs: Branch 6.8
INFO:build_docs: Branch 7.0
INFO:build_docs: Branch 7.1
INFO:build_docs: Branch 7.2
INFO:build_docs: Branch 7.3
INFO:build_docs: Branch 7.4
INFO:build_docs: Branch 7.5
INFO:build_docs: Branch 7.6
INFO:build_docs: Branch 7.7
INFO:build_docs: Branch 7.8
INFO:build_docs: Branch 7.9
INFO:build_docs: Branch 7.x
INFO:build_docs: Branch master
INFO:build_docs:All cross-document links OK
INFO:build_docs:Saving branch tracker
INFO:build_docs:Building sitemap
INFO:build_docs:Commiting changes
INFO:build_docs:Pushing changes
runbld>>> <<<<<<<<<<<< SCRIPT EXECUTION END <<<<<<<<<<<<
runbld>>> DURATION: 343004ms
runbld>>> STDOUT: 0 bytes
runbld>>> STDERR: 9895 bytes
runbld>>> WRAPPED PROCESS: SUCCESS (0)
runbld>>> Searching for build metadata in /var/lib/jenkins/workspace/elastic+docs+master+build
runbld>>> Storing build metadata:
runbld>>> Adding test report.
runbld>>> Searching for junit test output files with the pattern: TEST-.*\.xml$ in: /var/lib/jenkins/workspace/elastic+docs+master+build
runbld>>> Found 0 test output files
runbld>>> Test output logs contained: Errors: 0 Failures: 0 Tests: 0 Skipped: 0
runbld>>> Storing result
runbld>>> Store result: updated {:total 2, :successful 2, :failed 0} 2
runbld>>> BUILD: https://c150076387b5421f9154dfbf536e5c60.us-west1.gcp.cloud.es.io:9243/local-test-build-1531848254847/t/20200727130552-2EC64D96
runbld>>> NO MAIL GENERATED
Recording test results
None of the test reports contained any result
ERROR: [Google Cloud Storage Plugin] No artifacts found matching pattern: build/*.tar.bz2
[PostBuildScript] - [INFO] Executing post build scripts.
[elastic+docs+master+build] $ /bin/sh -xe /tmp/jenkins2336340937646013573.sh
+ curl -sS -X POST -H Content-Type: text/plain --data https://elasticsearch-ci.elastic.co/job/elastic+docs+master+build/2999/ https://homer.app.elstc.co/webhook/jenkins/build-finished
[WS-CLEANUP] Deleting project workspace...
[WS-CLEANUP] Deferred wipeout is used...
[WS-CLEANUP] done
Finished: SUCCESS
```

It's possible that this because the references to `shared/versions/stack/{version}.asciidoc` in conf.yaml aren't being correctly resolved for each version.