KVM-CI: Cleanup before cloning rusty-hermit

[mkroening]

I suspect, the reason for recent CI failures is that a KVM-CI-run did not complete and clean up after itself. So why not clean up, before cloning?

[codecov]

Codecov Report

Merging #125 (9b75b95) into master (1656e55) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #125   +/-   ##
=======================================
  Coverage   19.82%   19.82%           
=======================================
  Files          21       21           
  Lines        5190     5190           
=======================================
  Hits         1029     1029           
  Misses       4161     4161           

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[jounathaen]

This, and the fact that the runner only has 10GB of disk space, which I'm fixing right now ;-)

[bors]

Build succeeded:

• Build (macOS-latest, nightly)
• Build (ubuntu-latest, nightly)
• Format check (ubuntu-latest, nightly)
• KVM Tests
• Test (macOS-latest, nightly)
• Test (ubuntu-latest, nightly)