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/applier/workflow_engine/default.py

@@ -112,7 +112,7 @@ class DefaultWorkFlowEngine(base.BaseWorkFlowEngine):
 
             return flow
 
-        except exception.ActionPlanCancelled as e:
+        except exception.ActionPlanCancelled:
             raise
 
         except tf_exception.WrappedFailure as e: