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/functional/v2/test_readonly_glance.py

@@ -72,7 +72,7 @@ class SimpleReadOnlyGlanceClientTest(base.ClientTestBase):
         commands = []
         cmds_start = lines.index('Positional arguments:')
         cmds_end = lines.index('Optional arguments:')
-        command_pattern = re.compile('^ {4}([a-z0-9\-\_]+)')
+        command_pattern = re.compile(r'^ {4}([a-z0-9\-\_]+)')
         for line in lines[cmds_start:cmds_end]:
             match = command_pattern.match(line)
             if match: