Updated openstack/openstack
Project: openstack/oslo.serialization  472e6c901fe24bc9a179778e98a3874a59dade95

Fix coverage testing

Add coverage to test-requirements so that tox-e cover works - this
is part of the post jobs that are run.

Change-Id: I7b03b87ae3abab8bad96280ad8a23033c08df827