Fix new vtctl upgrade downgrade test on release-16.0

[frouioui]

Description

This PR implements proper filtering of the warning for vtctlclient. We will now remove the error produced by a missing or incorrect vtconfig on release-17.0 and above. This is useful to make the upgrade downgrade test pass.

[vitess-bot]

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[deepthi]

Looks fine to me.
One of the tests is still failing: Upgrade Downgrade Testing - Backups - Manual
Do we plan to fix that (either in this PR or separately)?

[frouioui]

Looks fine to me. One of the tests is still failing: Upgrade Downgrade Testing - Backups - Manual Do we plan to fix that (either in this PR or separately)?

This is planned in a subsequent PR.