Update hacking for Python3

The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.

Fix problems found.

Update local hacking checks for new flake8.

Remove hacking and friends from lower-constraints, they are not needed
to be installed at run-time.

Change-Id: Ia6af344ec8441dc98a0820176373dcff3a8c80d5

watcher/api/middleware/auth_token.py

@@ -34,7 +34,7 @@ class AuthTokenMiddleware(auth_token.AuthProtocol):
 
     """
     def __init__(self, app, conf, public_api_routes=()):
-        route_pattern_tpl = '%s(\.json|\.xml)?$'
+        route_pattern_tpl = r'%s(\.json|\.xml)?$'
 
         try:
             self.public_api_routes = [re.compile(route_pattern_tpl % route_tpl)