For lvm cinder, use Ptable that includes cinder-volumes

If cinder backend is LVM, set the controller hostgroup's Ptable
to Ptable.find_by_name('LVM with cinder-volumes').

This ptable should possibly be referenced by a Setting object at some point
rather than relying on name matching.

At this point if the PTable isn't found, we just silently ignore it,
since this isn't yet in the installer and I don't want staypuft blowing up
over it. Once this is in the installer, we can consider the proper way
of handling this if the Ptable doesn't exist.

On initial testing this seems to work when switching back and forth
between LVM and NFS cinder storage in non-HA, and also on switching
between HA and non-HA where the cinder change comes along for the
ride.