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/decision_engine/strategy/strategies/basic_consolidation.py

@@ -401,7 +401,7 @@ class BasicConsolidation(base.ServerConsolidationBaseStrategy):
         self._pre_execute()
 
         # backwards compatibility for node parameter.
-        if self.aggregation_method['node'] is not '':
+        if self.aggregation_method['node'] != '':
             LOG.warning('Parameter node has been renamed to compute_node and '
                         'will be removed in next release.')
             self.aggregation_method['compute_node'] = \