Fix and enable Hacking H501 warning

Enable Gating on H501. Fix the only two cases
that trigger.

Change-Id: Ib309b989df6556d7436e718e1497ce4dcacc83d6

heatclient/common/http.py

@@ -148,11 +148,13 @@ class HTTPClient(object):
             conn.request(method, conn_url, **kwargs)
             resp = conn.getresponse()
         except socket.gaierror as e:
-            message = "Error finding address for %(url)s: %(e)s" % locals()
+            message = ("Error finding address for %(url)s: %(e)s" %
+                       {'url': url, 'e': e})
             raise exc.InvalidEndpoint(message=message)
         except (socket.error, socket.timeout) as e:
             endpoint = self.endpoint
-            message = "Error communicating with %(endpoint)s %(e)s" % locals()
+            message = ("Error communicating with %(endpoint)s %(e)s" %
+                       {'endpoint': endpoint, 'e': e})
             raise exc.CommunicationError(message=message)
 
         body_iter = ResponseBodyIterator(resp)

tox.ini

@@ -22,6 +22,6 @@ downloadcache = ~/cache/pip
 
 [flake8]
 show-source = True
-ignore = H233,H302,H501
+ignore = H233,H302
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build