Migrate node backend app to GCE

This PR adds deployment of node backend app to GCE, at least until [Custom Runtime feature](https://www.youtube.com/watch?v=u3B1BhyXXdc) of App Engine is released.

Setup details are in `node/gce/README.md`.

@gauntface the project is already setup but I'll need your `google_compute_engine.pub` public ssh key.