Fix for JSON parse error on createNodesInGroup (JCLOUDS-558)

You're right, they are exactly the same. So I tried removing ServerInternal and had the following code.

    serverBase = apply((Server) context.deserialize(jsonElement, Server.class));

This caused a lovely StackOverflowError apparently because of the way the Gson deserializationContext works. I didn't bother digging to deep into it as it's the original code and not part of this change. I suspect the original author ran into the the StackOverflowError and ServerInternal was their way around it.