compute: RBD backend support

Since Havana, Nova is able to store VMs on RBD backend (ceph).

Change-Id: I17890a3e9e49572d989ad01383417b7256ef7e14
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "compute: RBD backend support"
Merge git://github.com/puppetlabs/puppetlabs-nova