Assure the socket file is removed before a restart

Otherwise, with latest nodejs, there will be no restart,
the socket will be in use.
remove socket file before listening on the socket

See

   https://github.com/joyent/node/issues/3540
   https://gist.github.com/9f93cdcd3a77b9142e51

for details on what's happening and why this is the fix.