[test] add flatcar image deletion to a top level catch block so even on an earlier failure the image gets cleaned up

[eljohnson92]

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.17%. Comparing base (39efc02) to head (e6de5f6).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #876   +/-   ##
=======================================
  Coverage   65.17%   65.17%           
=======================================
  Files          71       71           
  Lines        7957     7957           
=======================================
  Hits         5186     5186           
  Misses       2469     2469           
  Partials      302      302           

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