Examples: Correct VTAdmin Discovery File Path And Add Check

[mattlord]

Description

VTAdmin failing to discover the Vitess cluster in the local examples was reported in the Vitess Slack.

This was caused by the relative path usage missed as part of the refactoring done in: #12239

And this was easily missed because there was no check done to confirm proper discovery and thus the local examples CI tests did not fail.

In this PR we correct the static discovery file path AND add a check to ensure that the discovery was successful and if not, we exit with an error (which would cause the tests to fail).

Note While testing/confirming this fix in the CI with manual test re-runs, I saw another timing issue related to the specific healthy shard indicator that the scripts were using vs. what vtctld used in checking that a shard has a healthy serving primary tablet when e.g. executing ApplySchema (this was also reported in the Vitess Slack here). I changed the example scripts' healthy shard check to match with what vtctld uses. After that commit, the tests never failed.

Related Issue(s)

• Fixes: Bug Report: VTAdmin Does Not Show Any Resources With The Vitess Examples #12416
• Follow-up to: Examples: Add lib functions to wait for shard states #12239

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Documentation was added or is not required

[vitess-bot]

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[notfelineit]

Nice, love the added check 🥳