Fix: relayd: notify parent of readiness when all threads ready

- relayd start using daemonize common lib,
- wait for health check thread, listener and live listener threads to be
  ready before letting the parent know it is ready (in daemon and
  background modes).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>