Replace 'import json' with oslo_serialization

Replace remaining occurences of 'import json' with
'from oslo_serialization import jsonutils as json'
so pylint doesn't complain every time someone happens
to make a change to one of the modules that still
uses it.

Change-Id: Ife9f0fc54ad36887bdb939028f8903be16e590d6
diff --git a/neutron/tests/tempest/common/glance_http.py b/neutron/tests/tempest/common/glance_http.py
index 0a6f985..3d8c8aa 100644
--- a/neutron/tests/tempest/common/glance_http.py
+++ b/neutron/tests/tempest/common/glance_http.py
@@ -17,7 +17,6 @@
 
 import copy
 import hashlib
-import json
 import posixpath
 import re
 import socket
@@ -28,6 +27,7 @@
 
 import OpenSSL
 from oslo_log import log as logging
+from oslo_serialization import jsonutils as json
 from six import moves
 from six.moves import http_client as httplib
 from tempest_lib import exceptions as lib_exc