Updated openstack/openstack
Project: openstack/glance_store  6a45d7f9fb3ca5f2e6e21cd35c99d93c770aee7b

Add coverage to test-requirements.txt

This is needed for the post coverage job that executes tox -e cover.

Change-Id: I0b4c38fc48ef69343c389a589c5364443cb9e586