use jsonutils in oslo.serialization instead of keystoneclient

keystoneclient/openstack/common/jsonutils.py is removed in this patch
https://review.openstack.org/#/c/128454/
Now, we should use jsonutils in oslo.serialization package.

Change-Id: I7c8e8e6d5dffa85244368fd578616c9b19f4fd21
Merge "use jsonutils in oslo.serialization instead of keystoneclient"