cli: catch craft-provider errors

[mr-cal]

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• Have you signed the CLA?
• Have you successfully run make lint?
• Have you successfully run pytest tests/unit?

---

Cherry-pick the bugfix in #4295 onto hotfix/7.5

Related to #429
(CRAFT-2174)

[mr-cal]

Blocked by #4420

[codecov-commenter]

Codecov Report

Merging #4419 (63f2d79) into hotfix/7.5 (7cd7cba) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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@@             Coverage Diff             @@
##           hotfix/7.5    #4419   +/-   ##
===========================================
  Coverage       94.88%   94.88%           
===========================================
  Files             658      658           
  Lines           55162    55176   +14     
===========================================
+ Hits            52341    52355   +14     
  Misses           2821     2821           

Files	Coverage Δ
snapcraft/cli.py	82.69% <100.00%> (+0.69%)	⬆️
tests/unit/cli/test_exit.py	100.00% <100.00%> (ø)

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