The zuul.init and zuul-merger.init puppet module files did not check if
pidfiles existed when starting both services. The pidfile's might exist
in the event that the zuul-server and merger were killed, which doesn't
clean them up. This change checks for whether those files exist and notifies
the user to run the stop command which will clean up any residual pid files.
Change-Id: Ie65fdf372f1710ab0c32d03f6b359e1860f566db
b03adc90a8