Improve novaclient initialisation
Improve novaclient initialisation

Following advice from the folk in #openstack-nova, we should make some
small changes to how we use novaclient to prevent a breakage in the
future.

Change-Id: I71795b4267edc76bb8b6c0914521f913b6c643a9

openstack/horizon,yeming233/horizon,NeCTAR-RC/horizon,noironetworks/horizon,ChameleonCloud/horizon,yeming233/horizon,openstack/horizon,NeCTAR-RC/horizon,openstack/horizon,NeCTAR-RC/horizon,openstack/horizon,noironetworks/horizon,BiznetGIO/horizon,ChameleonCloud/horizon,BiznetGIO/horizon,yeming233/horizon,NeCTAR-RC/horizon,ChameleonCloud/horizon,noironetworks/horizon,BiznetGIO/horizon,noironetworks/horizon,BiznetGIO/horizon,ChameleonCloud/horizon,yeming233/horizon