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.

If the Ptable isn't found, we do two things:
1) on the wizard step 2, we display a warning (not error) message
   if the user chose non-HA
2) at the point where we try to set the lvm Ptable, we log an error

This situation will only occur in cases where someone is using staypuft
without having run the installer (so dev mode only)

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.
Merge pull request #206 from sseago/lvm-ptable

For lvm cinder, use Ptable that includes cinder-volumes