Every reactive charm that uses charms.openstack and implements unit
testing needs to mock charmhelpers, as otherwise the tests blow up.
This patch uses the mocking of charmhelpers in charms.openstack so that
a charm layer can just import test_mocks and charmhelpers will be mocked
out along with setting up a default
charmhelpers.c.o.u.OPENSTACK_RELEASES so that when an OpenStackCharm()
derived charm class won't fail on definition.
Change-Id: I489b15301f64310f7077d0e7246fd5e116877ed9
Related-Bug: #1693017
Depends-On: I5ac40617ee30e5f421ec16fc7592177a5e6aa166
Ryan Beisner