tests: Flaky e2e: TestQueryExternalPrefix

[bwplotka]

E.g: https://github.com/thanos-io/thanos/pull/3409/checks?check_run_id=1354006689#step:5:1480

Also, it would be nice to show logs only for failed tests.

[stale]

Hello 👋 Looks like there was no activity on this issue for the last two months.
Do you mind updating us on the status? Is this still reproducible or needed? If yes, just comment on this PR or push a commit. Thanks! 🤗
If there will be no activity in the next two weeks, this issue will be closed (we can always reopen an issue if we need!). Alternatively, use remind command if you wish to be reminded at some point in future.

[stale]

Closing for now as promised, let us know if you need this to be reopened! 🤗

[Abhishek357]

I am working on this and will open a PR soon.