Add rbd option to cinder configuration

Extend the support of cinder for rbd volume types by adding the
configuration variables needed (including parametrizing the
cinder_volume_driver to either 'iscsi' or 'rdb') and passing them on to
the cinder puppet module.

Change-Id: Id01e6346be85f9b4b70b11696b2395a09213ef05
Merge "Add rbd option to cinder configuration"