Tests: upgrade charm test upgrades all charms, not just the ones we're testing

When we run the zaza test to upgrade charm from stable to candidate, we are listing all applications and running charm upgrades. What we should do is limit that to a defined list of charms we're 'interested' in, so that candidate builds from other charm owners do not interefere with the tests.

Unless we agree that we should test the candidates alongside, say, the openstack team's candidate revisions. In which case, the releases need to be better coordinated with the other team.