Add hacking for code style checks

The following style checks are added:
 * do not use dict.iteritems
 * do not use dict.iterkeys
 * do not use dict.itervalues

Partial_implements: blueprint mistral-hacking

Change-Id: I25d846c80652d7746c3b958239797ce524ec235f

mistral_tempest_tests/tests/api/v2/test_tasks.py

@@ -12,6 +12,8 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import six
+
 from oslo_concurrency.fixture import lockutils
 from tempest import test
 
@@ -77,7 +79,7 @@ class TaskTypesTestsV2(base.TestCase):
         self.assertEqual(200, resp.status)
 
         bt = body['tasks']
-        ll = [[v for k, v in d.iteritems() if 'type' in k] for d in bt]
+        ll = [[v for k, v in six.iteritems(d) if 'type' in k] for d in bt]
         types_list = [item for sublist in ll for item in sublist]
 
         self.assertIn(