-v shows subprocess output

[minrk]

verbosity level 1 sets subprocess log level to debug (showing subprocess output), while level 2 sets all logging to debug-level. This solves the common problem of disabling suppression of setup.py output without being buried in debug output of getting dependencies from PyPI. Closes #8856.

requires -vv to enable full debug-level output, which is the current behavior of -v.

It would map more naturally to the multi-level -vvv to have more than one two log levels, as -vv currently produces exactly the same output as -v, as far as I can tell. But I expect that using custom log levels (e.g. 15 for VERBOSE) is probably not preferred? The python docs argue pretty strongly against custom log levels, but they are supported, if that seems better.

TODO:

• assign PR number to news file (need to open PR first!)
• update any affected tests
• decide if custom log level is preferred

[minrk]

Looking at the failing tests, I think this is resulting in undesirable behavior for commands other than install, since -v does nothing if no subprocesses are called. I think a custom log level approach (#9450) makes more sense and matches the expectation established by the -v[v] CLI much better.

[BrownTruck]

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[minrk]

Closing in favor of #9450