The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.
Fix problems found by updated hacking version.
Remove hacking and friends from lower-constraints, they are not needed
there at all.
Align lower-constraints for new pip [1]
Fix flake8 E305 and E117 and set W504 as ignored
[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-December/019285.html
Change-Id: Idae87291f4556eee77d40ab49f0d151435d70875