Fix gunicorn deployment to listen on preferred network

[jfischer]

To get things working, the new gunicorn fileserver listens on 0.0.0.0. We prefer to have it only listen on the ip address that will be given to clients. Need to think about the best way to do this. We might use the private ip if provided in the host resource. In that case, we probably should use the same logic as djm - add public ip, hostname, and private ip to the definition and use priority order to select a default.

Also need to think about how to coordinate the url generation in the code with the listen address. One option is just to write out the bind address to a well-known file.