The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.
Fix problems found.
Remove hacking and friends from lower-constraints, they are not needed
for installation.
Change-Id: Ia16e8cbccf7b38be8909aa94e66c04b99f200b89
(cherry picked from commit 2ebc766534eba6163e98b94a1f114ece18739fff)