The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.
Fix problems found by updated hacking version.
Update local hacking checks for new flake8.
Remove hacking and friends from lower-constraints, they are not
needed in installations.
Currently, we have hacking check in kolla, but no place where we
can define hacking check rules. This patch adds HACKING.rst file
for that. And also add test cases for hacking.