Problem with yamllint configuration file

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Processing a repository which does not have specified rules in `.yamllint` configuration file will result in:

```
Called from /root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/activesupport-4.2.10/lib/active_support/dependencies.rb:240:in `load_dependency'
2018-04-21T12:59:14.996Z 3748 TID-grgzknuxk CommitMonitorHandlers::CommitRange::RubocopChecker JID-5e5788c93fcadd6dc8e7ba96 INFO: fail: 3.448 sec
2018-04-21T12:59:14.997Z 3748 TID-grgzknuxk WARN: {"class":"CommitMonitorHandlers::CommitRange::RubocopChecker","args":[2,["265235e76fa59718486c042a0650443d18400e6e"]],"retry":true,"queue":"miq_bot_glacial","jid":"5e5788c93fcadd6dc8e7ba96","created_at":1524315367.5318902,"enqueued_at":1524315551.5467553,"error_message":"undefined method `captures' for nil:NilClass\nDid you mean? capture","error_class":"NoMethodError","failed_at":1524315372.3904035,"retry_count":1,"retried_at":1524315554.9960437}
2018-04-21T12:59:14.997Z 3748 TID-grgzknuxk WARN: NoMethodError: undefined method `captures' for nil:NilClass
Did you mean? capture
2018-04-21T12:59:14.997Z 3748 TID-grgzknuxk WARN: /root/miq_bot/lib/linter/yaml.rb:44:in `line_to_hash'
/root/miq_bot/lib/linter/yaml.rb:7:in `block in parse_output'
/root/miq_bot/lib/linter/yaml.rb:7:in `collect'
/root/miq_bot/lib/linter/yaml.rb:7:in `parse_output'
/root/miq_bot/lib/linter/base.rb:31:in `run'
/root/miq_bot/app/workers/concerns/code_analysis_mixin.rb:26:in `run_all_linters'
/root/miq_bot/app/workers/concerns/code_analysis_mixin.rb:12:in `merged_linter_results'
/root/miq_bot/app/workers/commit_monitor_handlers/commit_range/rubocop_checker.rb:25:in `process_branch'
/root/miq_bot/app/workers/commit_monitor_handlers/commit_range/rubocop_checker.rb:19:in `perform'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:152:in `execute_job'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:134:in `block (2 levels) in process'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/chain.rb:128:in `block in invoke'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidetiq-0.7.2/lib/sidetiq/middleware/history.rb:8:in `call'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/chain.rb:130:in `block in invoke'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/server/active_record.rb:6:in `call'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/chain.rb:130:in `block in invoke'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/server/retry_jobs.rb:74:in `call'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/chain.rb:130:in `block in invoke'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/server/logging.rb:11:in `block in call'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/logging.rb:32:in `with_context'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/server/logging.rb:7:in `call'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/chain.rb:130:in `block in invoke'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/middleware/chain.rb:133:in `invoke'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:129:in `block in process'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:168:in `stats'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:128:in `process'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:80:in `process_one'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/processor.rb:68:in `run'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/util.rb:17:in `watchdog'
/root/.rbenv/versions/2.3.6/lib/ruby/gems/2.3.0/gems/sidekiq-4.1.4/lib/sidekiq/util.rb:25:in `block in safe_thread'
```

**NOTE**: yamllint has its default rules see [here](https://yamllint.readthedocs.io/en/stable/configuration.html#default-configuration).

The problem starts at [line number 7 in `lib/linter/yaml.rb`](https://github.com/ManageIQ/miq_bot/blob/master/lib/linter/yaml.rb#L7):

```ruby
parsed = lines.collect { |line| line_to_hash(line) }
```

```
[1] pry(#)> lines
=> ["{\"files\":[{\"path\":\"\\\\*\\\\*\",\"offenses\":[{\"severity\":\"fatal\",\"message\":\"Linter::Yaml STDERR:\\n```\\ninvalid config: not a dict\\n\\n```\",\"cop_name\":\"Linter/Yaml\"}]}],\"summary\":{\"offense_count\":1,\"target_file_count\":3,\"inspected_file_count\":3}}"]
```

in `line_to_hash(line)` at:

```ruby
severity, message = severity_message.match(/\[(.*)\] (.*)/).captures
```

where `.captures` is called on `nil:NilClass`:

```
[3] pry(#)> severity_message
=> "[{\"severity\":\"fatal\",\"message\":\"Linter::Yaml STDERR:\\n```\\ninvalid config: not a dict\\n\\n```\",\"cop_name\":\"Linter/Yaml\"}]}],\"summary\":{\"offense_count\":1,\"target_file_count\":3,\"inspected_file_count\":3}}"
```

```
[4] pry(#)> severity_message.match(/\[(.*)\] (.*)/)
=> nil
```

**Related issue**: https://github.com/ManageIQ/miq_bot/issues/392

Start in lib/linter/yaml.rb, especially line 7 where lines are parsed and line 44 where the severity message is matched. Reproduce processing a repository without specified yamllint rules and inspect the resulting linter output. Done means this configuration is handled without the NoMethodError and the linter result remains usable.

Written by the indexing model from the issue text.