Add tests for metadata updates
Add tests for metadata updates

This change adds couple of unit tests to persistence base test case,
to verify that metadata updates are not lost.

Change-Id: I467b21eb59e9b85a689086d09c775b714a70d02a

citrix-openstack-build/taskflow,citrix-openstack-build/taskflow,openstack/taskflow,junneyang/taskflow,jimbobhickville/taskflow,varunarya10/taskflow,junneyang/taskflow,openstack/taskflow,varunarya10/taskflow,pombredanne/taskflow-1,pombredanne/taskflow-1,jimbobhickville/taskflow