Don't unmount kubelet-root-dir on k0s reset

[dockerpac]

Description

Fixes an issue where k0s reset was unmounting and deleting the kubelet-root-dir mount point when configured on a separate filesystem.

When --kubelet-root-dir is on a dedicated partition (common in production), k0s reset would unmount the filesystem and delete the mount point.

This PR applies the same mount point preservation logic to kubelet-root-dir that was already existing for data-dir.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Manual test
• Auto test added

Tested scenarios:

• Mounted filesystem: Kubelet mount point preserved, only contents deleted
• Default setup: Directory completely removed as before

Checklist

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[jnummelin]

@ncopa You were involved designing the data-dir reset/unmount logic, could you review this? 🙏

[ncopa]

The make check-reset test fails:

        	Test:       	TestResetSuite/TestReset/k0s_reset
        	Messages:   	/var/lib/kubelet still exists