rbd : create_base

rbd : create_base

- rename volume
- take snapshot '__base__'
- protect the snapshot

Fix: the volume_snapshot sub need a $running parameter,
to known if it need to use rbd command or qmp command to take the snapshot.
for now, I pass undef, as it should be always offline.

(But we need to verify somewhere that vm is not running,
because take a snapshot with rbd command on a running vm can break it.

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>