Switch remaining json import to oslo_serialization

While switching json to oslo_serialization, there were some
usage of json left which are caught while implementing UT for
service clients.

- http://logs.openstack.org/73/214073/4/check/gate-tempest-python34/0976c0c/testr_results.html.gz

This commit switch all remaining json usage to jsonutils of
oslo_serilization

Change-Id: Icb38fd22c61545cfbe024108a06068ada01afc6b
4 files changed