Ported the Rackspace DNS and its tests to the one-class approach.

This probably isn't merge ready:

- [ ] totally breaks backwards compatibility (I'll reintroduce the compatibility aliases once I verify this is the right approach)
- [ ] I'm not convinced this actually works (maybe I'm wrong though!)
- [ ] It could really use a thorough review

So let me know what you think and I'll add the backwards compat aliases (if needed) once everything else looks ok.