Switch all uses of json to oslo_serialization

This commit migrates all the usage of the json library to use jsonutils
from oslo_serialization. On python 3 httplib2 returns a bytes type for
the response body however all the methods in the json library are
expecting str types. We could switch all the uses of json.loads to
encode the input prior to calling json.loads however oslo_serialization
has baked in all dual python version edge conditions around this into
a call compatible lib which is much cleaner.

Change-Id: Icee30fb74db128c77b2c0c27e68b5801bd138cd5
diff --git a/tempest/services/volume/json/qos_client.py b/tempest/services/volume/json/qos_client.py
index 37ab9cd..e3d6a29 100644
--- a/tempest/services/volume/json/qos_client.py
+++ b/tempest/services/volume/json/qos_client.py
@@ -12,9 +12,9 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import json
 import time
 
+from oslo_serialization import jsonutils as json
 from tempest_lib import exceptions as lib_exc
 
 from tempest.common import service_client