release-26.2.7-rc: roachtest: admission-control/index-backfill/no-disk-limit failed

roachtest.admission-control/index-backfill/no-disk-limit [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21501540?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21501540?buildTab=artifacts#/admission-control/index-backfill/no-disk-limit) on release-26.2.7-rc @ [b1582e0a72ed7f3813a4346a2ddce2d9a29c30c2](https://github.com/cockroachdb/cockroach/commits/b1582e0a72ed7f3813a4346a2ddce2d9a29c30c2):

Failed with:

```
(test_runner.go:2727).func1: task ``copy-snapshot-n3`` returned error: n3: failed to create disk from snapshot: COMMAND_PROBLEM: exit status 1
(admission_control_index_backfill.go:222).runIndexBackfill: unable to download node_exporter: context canceled
test artifacts and logs in: /artifacts/admission-control/index-backfill/no-disk-limit/run_1
```
Cluster Node to Ip Mapping:
| Node | Public IP | Private IP |
| --- | --- | --- |
| teamcity-21501540-1788584904-11-n10cpu8-0001 | | 10.91.99.2 |
| teamcity-21501540-1788584904-11-n10cpu8-0002 | | 10.91.98.251 |
| teamcity-21501540-1788584904-11-n10cpu8-0003 | | 10.91.98.255 |
| teamcity-21501540-1788584904-11-n10cpu8-0004 | | 10.91.99.6 |
| teamcity-21501540-1788584904-11-n10cpu8-0005 | | 10.91.98.253 |
| teamcity-21501540-1788584904-11-n10cpu8-0006 | | 10.91.99.0 |
| teamcity-21501540-1788584904-11-n10cpu8-0007 | | 10.91.99.4 |
| teamcity-21501540-1788584904-11-n10cpu8-0008 | | 10.91.98.254 |
| teamcity-21501540-1788584904-11-n10cpu8-0009 | | 10.91.99.7 |
| teamcity-21501540-1788584904-11-n10cpu8-0010 | | 10.91.99.254 |

Parameters:
- arch=amd64
- cloud=gce
- coverageBuild=false
- cpu=8
- diskCount=0
- encrypted=false
- fs=ext4
- localSSD=false
- runtimeAssertionsBuild=false
Help

See: [roachtest README](https://github.com/cockroachdb/cockroach/blob/master/pkg/cmd/roachtest/README.md)

See: [How To Investigate \(internal\)](https://cockroachlabs.atlassian.net/l/c/SSSBr8c7)

See: [Grafana](https://go.crdb.dev/roachtest-grafana/teamcity-21501540/admission-control-index-backfill-no-disk-limit/1788585389380/1788585663132)

Same failure on other branches

- #173551 release-26.2.6-rc: roachtest: admission-control/index-backfill/no-disk-limit failed [A-admission-control A-testing C-bug C-test-failure O-roachtest O-robot P-3 T-kv branch-release-26.2.6-rc]
- #173393 release-26.2: roachtest: admission-control/index-backfill/no-disk-limit failed [A-testing C-bug C-test-failure O-roachtest O-robot P-3 T-kv branch-release-26.2]

/cc @cockroachlabs/admission-control

[This test on roachdash](https://roachdash.crdb.dev/?filter=status:open%20t:.*admission-control/index-backfill/no-disk-limit.*&sort=title+created&display=lastcommented+project) | [Improve this report!](https://github.com/cockroachdb/cockroach/tree/master/pkg/cmd/bazci/githubpost/issues)

Jira issue: CRDB-67936

Start with pkg/cmd/roachtest/README.md and the artifacts at /artifacts/admission-control/index-backfill/no-disk-limit/run_1. Trace copy-snapshot-n3 in test_runner.go and runIndexBackfill in admission_control_index_backfill.go, focusing on the disk-creation error and canceled node_exporter download. Done means the no-disk-limit roachtest completes successfully on the affected release branch.

Written by the indexing model from the issue text.