Exit the process on EOADDRINUSE

The web service we start up in rt testing occasionally runs into port
conflicts. Error returns are handled by restarting the service on a different
random port. Using cluster.worker.disconnect() however prevented an error from
being returned and thus left the rt test clients in a non-working state.

Change-Id: Ieb95de9a7a81e5f8e512637a924563f5dc0feb2e