build providers: destroy on create failures

[sergiusens]

When launch fails within the context manager, there is not logic that
ensures the build provider is actually destroyed so the VM does not
stay running.

LP: #1792242

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• If this is a bugfix. Have you checked that there is a bug report open for the issue you are trying to fix on bug reports?
• If this is a new feature. Have you discussed the design on the forum?
• Have you successfully run ./runtests.sh static?
• Have you successfully run ./runtests.sh tests/unit?

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[kyrofa]

+78 −31 😞

[sergiusens]

mostly tests :-)

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@eafd6d6). Click here to learn what that means.
The diff coverage is 93.33%.

@@            Coverage Diff            @@
##             master    #2374   +/-   ##
=========================================
  Coverage          ?   90.29%           
=========================================
  Files             ?      196           
  Lines             ?    12742           
  Branches          ?     1924           
=========================================
  Hits              ?    11505           
  Misses            ?      840           
  Partials          ?      397

Impacted Files	Coverage Δ
...apcraft/internal/build_providers/_base_provider.py	87.12% <100%> (ø)
snapcraft/internal/build_providers/errors.py	97.05% <100%> (ø)
.../internal/build_providers/_multipass/_multipass.py	84.34% <81.81%> (ø)

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