Apply rules set by https://gerrit-review.googlesource.com/c/git-repo/+/362954/ across the codebase and fix any lingering errors caught
by flake8. Also check black formatting in run_tests (and CQ).
Bug: b/267675342
Change-Id: I972d77649dac351150dcfeb1cd1ad0ea2efc1956
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/363474
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>