Fix cleanup manual rollback

[pchila]

What does this PR do?

This PR fixes the relative path calculation for agent versioned homes to preserve introduced with #9643.
Removes ambiguity in what a path to a versioned home to preserve should look like: it should always be data/elastic-agent-<variable unique version part here>.

Adds a few checks and resolves the relative path when calling rollback from command line.

Why is it important?

To preserve elastic-agent versioned home directories correctly during cleanup.

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

How to test this PR locally

Related issues

• Relates Manual rollback after grace period #9643

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[mergify]

This pull request does not have a backport label. Could you fix it @pchila? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-./d./d is the label that automatically backports to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b fix-cleanup-manual-rollback upstream/fix-cleanup-manual-rollback
git merge upstream/main
git push upstream fix-cleanup-manual-rollback

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 41d1b6a

Failed CI Steps

• x86_64:sudo: fleet

History

• 💛 Build #31120 was flaky 18c8b79
• 💛 Build #30867 was flaky ca32577
• 💔 Build #30805 failed ca7c7ba
• 💔 Build #30764 failed 6798437
• 💔 Build #30625 failed 174f2e4
• 💔 Build #30497 failed af2a6d5

cc @pchila