Make flake8 ignore list more fine granular

Instead of ignoring all flake8 specific errors ("F"), list those
codes that currently fail so that they can be addressed one by one
and the currently passing ones will not get added by accident.

Change-Id: Ia40f0d832b70eeb788ae14a84dc0c40cc2e4724f
Merge "Make flake8 ignore list more fine granular"