Removed _dead.wait from the stop method and added a wait method to
explicitly wait for graceful shutdown. Implicitly waiting for
graceful shutdown in the stop method is leading to potential
deadlock situations when conductor is running in the main thread
and a signal handler is used to kick off stop/shutdown.
Also in larger systems, it is desirable to be able to initiate
shutdown on all running services then wait/join everything together
so as not to force a serial shutdown pattern.
Change-Id: Ic74dab22b09100c5b653d12c2518f83a1bf8e859
e7df6c66f0