Run remote interpreter process in remote machine

For now, all the remote interpreter process are running in the same host as zeppelin server, this is fine for single user. But after we support multiple users, there would be many remote interpreter process on the same host as each user would run its own interpreter process, I have concern about the scalability. So it would be better to run them on a remote host. One candidate solution is to run them as yarn application. This would be a big change, need design review before implementation.