The repo is Python using both Python 2 and 3 now, so update hacking to
version 2.0 which supports Python 2 and 3. Note that latest hacking
release 3.0 only supports version 3.
Fix problems found.
Remove hacking and friends from lower-constraints, they are not needed
for installation.
Change-Id: I9bd913ee1b32ba1566c420973723296766d1812f
96b56519bf