Update Nova driver's list_instance_uuids()

list_instance_uuid() was dependent on list_instances().  The latter
was fixed to return the correct results but the former was not,
causing nova-compute start up failures.  This updates it accordingly
to return the expected output via a client API call.

Change-Id: I27651ca01dbdcc95ca729da7dbbeafdc616eec4e
Closes-bug: #1326988
Merge "Update Nova driver's list_instance_uuids()"