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/controllers/v1/types.py

@@ -184,7 +184,7 @@ class MultiType(wtypes.UserType):
 class JsonPatchType(wtypes.Base):
     """A complex type that represents a single json-patch operation."""
 
-    path = wtypes.wsattr(wtypes.StringType(pattern='^(/[\w-]+)+$'),
+    path = wtypes.wsattr(wtypes.StringType(pattern=r'^(/[\w-]+)+$'),
                          mandatory=True)
     op = wtypes.wsattr(wtypes.Enum(str, 'add', 'replace', 'remove'),
                        mandatory=True)

watcher/api/controllers/v1/versions.py

@@ -25,6 +25,7 @@ class VERSIONS(enum.Enum):
     MINOR_4_WEBHOOK_API = 4  # v1.4: Add webhook trigger API
     MINOR_MAX_VERSION = 4
 
+
 # This is the version 1 API
 BASE_VERSION = 1
 # String representations of the minor and maximum versions

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)