Cloud Networking

PR for Rackspace networking. Unfortunately, it looks like none of the Rackspace operations for this service can be delegated to the Openstack Neutron code due to differences in URLs and `Network` objects.

- [x] Networks
 - [X] Operations
 - [X] Unit Tests
 - [x] Acceptance Tests
- [x] Virtual Interfaces
 - [X] Operations
 - [X] Unit Tests
 - [x] Acceptance Tests 
The more I use this way of setting the client, the more I dislike it because it relies on global state and often introduces errors if it's not set correctly (i.e. if you forgot to put `Setup()` at the top of your test). What do you think about returning the client as a value:

```go
func TestFoo(t *testing.T) {
   client := setup(t) // We _definitely_ know it's set

   testListFoo(t, client)
}
```

But you'd then need to inject it into every other function in the test file (which is more explicit, but repetitive). Just an idea.