image-tools: T5758: restore saving previous data on install

[jestabro]

Change Summary

Restore scanning previous installations for config data and ssh host keys on install.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):
  -- missing functionality of revision

Related Task(s)

• https://vyos.dev/T5758

Related PR(s)

Component(s) name

Proposed changes

How to test

Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[c-po]

I think a rebase operation went sideways as you include a commit (6d6b3fb) from @nicolas-fort.

Can you please rebase to the latest current version?

[jestabro]

I think a rebase operation went sideways as you include a commit (6d6b3fb) from @nicolas-fort.

Can you please rebase to the latest current version?

Thanks, @c-po !