release-26.2.7-rc: roachtest: admission-control/index-backfill/provisioned-bandwidth=false failed

roachtest.admission-control/index-backfill/provisioned-bandwidth=false [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21499540?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21499540?buildTab=artifacts#/admission-control/index-backfill/provisioned-bandwidth=false) on release-26.2.7-rc @ [b1582e0a72ed7f3813a4346a2ddce2d9a29c30c2](https://github.com/cockroachdb/cockroach/commits/b1582e0a72ed7f3813a4346a2ddce2d9a29c30c2):

Failed with:

```
(test_runner.go:2727).func1: task ``copy-snapshot-n4`` returned error: n4: 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/provisioned-bandwidth=false/run_1
```
Cluster Node to Ip Mapping:
| Node | Public IP | Private IP |
| --- | --- | --- |
| teamcity-21499540-1788544345-10-n10cpu8-0001 | | 10.91.100.140 |
| teamcity-21499540-1788544345-10-n10cpu8-0002 | | 10.91.100.147 |
| teamcity-21499540-1788544345-10-n10cpu8-0003 | | 10.91.100.148 |
| teamcity-21499540-1788544345-10-n10cpu8-0004 | | 10.91.100.141 |
| teamcity-21499540-1788544345-10-n10cpu8-0005 | | 10.91.100.145 |
| teamcity-21499540-1788544345-10-n10cpu8-0006 | | 10.91.100.144 |
| teamcity-21499540-1788544345-10-n10cpu8-0007 | | 10.91.100.146 |
| teamcity-21499540-1788544345-10-n10cpu8-0008 | | 10.91.100.143 |
| teamcity-21499540-1788544345-10-n10cpu8-0009 | | 10.91.100.142 |
| teamcity-21499540-1788544345-10-n10cpu8-0010 | | 10.91.98.25 |

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-21499540/admission-control-index-backfill-provisioned-bandwidth-false/1788544749393/1788544989151)

Same failure on other branches

- #173552 release-26.2.6-rc: roachtest: admission-control/index-backfill/provisioned-bandwidth=false 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]
- #173394 release-26.2: roachtest: admission-control/index-backfill/provisioned-bandwidth=false failed [A-admission-control 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/provisioned-bandwidth=false.*&sort=title+created&display=lastcommented+project) | [Improve this report!](https://github.com/cockroachdb/cockroach/tree/master/pkg/cmd/bazci/githubpost/issues)

Jira issue: CRDB-67904

Start with the TeamCity log and artifacts under /artifacts/admission-control/index-backfill/provisioned-bandwidth=false/run_1, then read admission_control_index_backfill.go around line 222 and test_runner.go around line 2727. Compare the repeated failures in #173552 and #173394 and consult the roachtest README; done means the cause is addressed and this scenario passes on the affected release branches.

Written by the indexing model from the issue text.