Adds rackspace cloudnetworks-us provider

> Why exactly is there a rush to get this in
There seems to be a lot of interest (user-side) in neutron. The approach here, while unarguably ugly, does not affect users, but provides extra functionality in the form of additional compatibility. It also avoids modifying core jclouds and keeps the fix within a Beta API.

> Pay for new code by fixing other vs continually add to the pile.
Valid concerns. This PR proposes a trade-off that you disagree with.

> Somehow you get the idea that my statement isn't blocking.
Where did I say that? I was trying to explain the technical reasoning behind this approach. It would be much more difficult to get people to discuss it (or propose a more elegant solution) without a PR. There seems to be some confusion here - apologies.