Ensure DC/OS Erlang based apps use dcos-epmd.service

Currently it is possible for spartan to start it's own epmd if dcos-epmd is not yet started or has died for some reason. The systemd services for each of the Erlang based components should be reviewed and modified so that each ensures dcos-epmd is already running before starting.

Additionally, although unlikely, if dcos-epmd should ever die, the Erlang based apps need to be restarted so that they are registered for future communications.