Enable flake8 H303,H304 checking

We had two types of wildcard imports in the code. Unneeded ones
in test files that are just removed, and some that we actually
want which are kept using the '#noqa' comment to tell flake8
to skip specific checks (such as H303) for that line.

Change-Id: I7d194a7bbcccdba419a2a49a919e17c047633cf0