Remove all usage of six library

Replace six with Python 3 style code.

Change-Id: Ie0da4c882847268a58ab20f0fbc82fc8cf658297
diff --git a/cinder_tempest_plugin/services/consistencygroups_client.py b/cinder_tempest_plugin/services/consistencygroups_client.py
index a29a90a..cea99ed 100644
--- a/cinder_tempest_plugin/services/consistencygroups_client.py
+++ b/cinder_tempest_plugin/services/consistencygroups_client.py
@@ -14,10 +14,10 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import http.client as http_client
 import time
 
 from oslo_serialization import jsonutils as json
-from six.moves import http_client
 from tempest.lib.common import rest_client
 from tempest.lib import exceptions as lib_exc