Update the Nova client creation
Update the Nova client creation

The current novaclient creation code passes in a url parameter which
isn't valid. This change updates the client creation and uses the same
code as Mistral does for it's own OpenStack actions.

Change-Id: Id72cefcb7a1bd9baf515dd95f389d206a3ccf01a
Closes-bug: #1665637

openstack/tripleo-common,openstack/tripleo-common