@spackbot fix style

Let me see if I can fix that for you!

I was able to run spack style --fix for you!

==> Running style checks on spack
  selected: isort, black, flake8, mypy
==> Modified files
  lib/spack/spack/binary_distribution.py
  lib/spack/spack/cmd/buildcache.py
  lib/spack/spack/cmd/ci.py
  lib/spack/spack/test/bindist.py
==> Running isort checks
  isort checks were clean
==> Running black checks
All done! ✨ 🍰 ✨
4 files left unchanged.
  black checks were clean
==> Running flake8 checks
lib/spack/spack/test/bindist.py:473: [E722] do not use bare 'except'
lib/spack/spack/test/bindist.py:482: [E722] do not use bare 'except'
lib/spack/spack/test/bindist.py:501: [E722] do not use bare 'except'
lib/spack/spack/test/bindist.py:511: [E722] do not use bare 'except'
  flake8 found errors
==> Running mypy checks
Success: no issues found in 586 source files
  mypy checks were clean

I wasn't able to make any further changes, but please see the message above for remaining issues you can fix locally!

Push failure results in pipeline failure berkeley-db
Reindex fails when unable to list keys reindex

Successful push and usage of packages diffutils

There are a lot of basic issues with this PR. Can you improve it?

@haampie are you okay with these changes? I would like to get this in sooner than later.

@haampie I took another pass on this with fresh eyes. I think because all of these APIs are internal the required flag to maintain the old, non-signaling failure behavior was not really worth it.

I added new exceptions, GenerateIndexError and PushToBuildCacheError, and simply raise the error and the message to the next level to be handled. This seems to work well and l think it is a much cleaner solution.

The two code paths mentioned by @haampie should be tested now. Letting the coverage run to verify and will clean up the commit history after.

lgtm, but please remove the unused bits

removed debug, rebased to fix merge conflict