bdk: add CLI argument parsing unittests.

I'm going to be looking into changing our argument parsing to try to
fix some corner cases that don't behave the way we want. This is just a
preliminary CL to add some unit tests to make sure the upcoming changes
don't break existing behavior.

Also some minor style fixes for files I'm touching anyway.

Bug: 27795688
Test: python test_runner.py
Test: various bdk2 commands to make sure they work the same.
Change-Id: I6b46bc385c412399275ff8ef9cd8b1409ecc5689
9 files changed