Add nodes dynamically to an AppScale deployment

Contacts the AppController to dynamically add nodes to an already running AppScale deployment. Relies on new SOAP methods in the AppController (https://github.com/AppScale/appscale/pull/163).

To test, try following the documentation (https://github.com/AppScale/appscale/wiki/Adding-Machines-to-an-AppScale-Deployment) and verifying that it works. That document adds two nodes to an existing four node deployment in VirtualBox.