The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.
Fix problems found.
Update local hacking checks for new flake8.
Remove hacking and friends from lower-constraints, they are not needed
to be installed at run-time.
Fix flake8wrap to take arguments from tox.ini and not look at .tox
directory.
Change-Id: I1c5f5a85af02d9f11e475b6088fe1d9d9d252083
3fe89808c6