multi rbd: add opts, deprecate glance_api_version

- Add all cinder rbd params (multi-backends)
- Update documentation/tests
- Deprecate glance_api_version to avoid duplicate definition
  with cinder::glance class.
  (use glance_api_version of cinder::glance class instead.)

Change-Id: I957d81647cd0320a52be00dceff23692ba208017