test_runner: fix tenant_get_shards with one pageserver

[erikgrinaker]

Problem

tenant_get_shards() does not work with a sharded tenant on 1 pageserver, as it assumes an unsharded tenant in this case. This special case appears to have been added to handle e.g. test_emergency_mode, where the storage controller is stopped. This breaks e.g. the sharded ingest benchmark in #9591 when run with a single shard.

Summary of changes

Correctly look up shards even with a single pageserver, but add a special case that assumes an unsharded tenant if the storage controller is stopped and the caller provides an explicit pageserver, in order to accomodate test_emergency_mode.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[jcsp]

LGTM - the fast path for one pageserver dates from the early days of multiple pageservers + migrations -- these days its just a footgun.

[github-actions]

5328 tests run: 5106 passed, 0 failed, 222 skipped (full report)

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Flaky tests (1)

Postgres 17

• test_tenant_config: debug-x86-64

Code coverage* (full report)

• functions: 31.5% (7768 of 24690 functions)
• lines: 48.9% (61021 of 124672 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
3072b6d at 2024-11-01T11:18:20.831Z :recycle:}