Set the default gnocchi driver to swift
Set the default gnocchi driver to swift

Until mitaka we have been using file driver. Swift is much more
scalable so lets use that instead as the default.

Change-Id: Idb0d55f99dbdd9d89881ce981d489756eb508fc0

dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,trozet/opnfv-tht,trozet/opnfv-tht,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,trozet/opnfv-tht