Update json module to jsonutils

oslo project provide jsonutils, and ironic-tempest-plugin use it
in many place[1], this PS to update the remained json moudule to
 oslo jsonutils for consistency.

[1]: https://github.com/openstack/ironic-tempest-plugin/search?utf8=%E2%9C%93&q=jsonutils&type=

Change-Id: I76daaca9e6de990949994915c9d6709de4a67f9b

ironic_tempest_plugin/tests/scenario/introspection_manager.py

@@ -10,10 +10,11 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import json
 import os
 import time
 
+from oslo_serialization import jsonutils as json
+
 import six
 import tempest
 from tempest import config