s6: Use s6-svc -Dd to stop services

This allows us to get rid of the sleep call in the stop function. Also,
we set a configurable timeout value for stopping daemons.

sh/s6.sh

@@ -31,11 +31,7 @@ s6_stop()
  fi
 	s6_service_link="${RC_SVCDIR}/s6-scan/${s6_service_path##*/}"
 	ebegin "Stopping ${name:-$RC_SVCNAME}"
-	s6-svc -d "${s6_service_link}"
-	if [ -n "$s6_svwait_options_stop" ]; then
-		s6-svwait ${s6_svwait_options_stop} "${s6_service_link}"
-	fi
-	sleep 1.5
+	s6-svc -Dd -T ${s6_service_timeout_stop:-10000} "${s6_service_link}"
 	set -- $(s6-svstat "${s6_service_link}")
 	[ "$1" = "down" ]
 	eend $? "Failed to stop $RC_SVCNAME"