Update hacking for Python3

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: I5ae47a7b11ff29a301e440c15daf30db7738485b

glanceclient/tests/unit/v2/test_shell_v2.py

@@ -55,6 +55,8 @@ def schema_args(schema_getter, omit=None):
             'locations': {'type': 'string'},
             'copy_from': {'type': 'string'}}}
     return original_schema_args(my_schema_getter, omit)
+
+
 utils.schema_args = schema_args
 
 from glanceclient.v2 import shell as test_shell  # noqa