Fix and enable gating on H501

This enables the following checks:

H404 - multi line docstring should start without a leading new line
H501 - Do not use locals() for string formatting
F403 - ‘from module import *’ used; unable to detect undefined names
F811 - redefinition of unused name from line N

Change-Id: Ib5f1ab2ffb762cc4795c2576750688342213d752