Ceph RBD integration for openstack-block-storage

This allows using a Ceph cluster as cinder backend.  The necessary
dependencies are defined in platform_options['cinder_ceph_packages'] and
can be overridden.

Overall documentation on Ceph integration has to be added, I'd be glad
to help with that.

This changes the way secrets are handled:

openstack[block-storage][rbd_secret_name]  will fetch the secret uuid
shared between cinder and nova from the databag with that name and set the
openstack[block-storage][rbd_secret_uuid] attribute.

Besides that, the user is expected to provide the password for the cephx
user, `rbd_user`, used with the pool `rbd_pool`, in the data bag item
`rbd_key_name` in the service password data bag.

Implements: blueprint rbd-for-block-storage

Change-Id: Iafe2bdea0d6120bb08c027482c94d819a67aee4a
Merge "Ceph RBD integration for openstack-block-storage"