Fix the tests

@liveh2o @localshred 
@tamird, I cannot. It definitely shouldn't happen. Your thinking is spot on in that regard. All I can say for certain is that without `exit 0` the process hangs indefinitely on shutdown in one of our production apps. Unless I'm mistaken, having an `exit 0` at the end of `bin/rpc_server` is about as impactful as a comment would be. Do you agree?