Miscellaneous fixes to:
- Handling of Ceph drives now works end-to-end (RHBZ#1026688).
- In particular, you can now use rbd:/// URIs in guestfish (and
they work).
- Parse Ceph & NBD network drives from libvirt XML correctly, so
that existing domains with Ceph/NBD drives can be added
(eg. using guestfish -d option).
- Add more testing of the above.