fix 'rbd showmapped' for ceph mimic
fix 'rbd showmapped' for ceph mimic

The json ouput changed from list to dict
* http://docs.ceph.com/docs/master/releases/mimic/ - The rbd CLI’s
showmapped JSON and XML output has changed.)

mbakke/ganeti,mbakke/ganeti,ganeti/ganeti,mbakke/ganeti,ganeti/ganeti,ganeti/ganeti