om-watchdog: Stop om-watchdog via procd before rebooting

It was noticed that the system can hang during the reboot before the kernel
actually triggers the system reset and before all processes are stopped. The
watchdog didn't automatically restart the system because the om-watchdog
process was still running and triggering the hardware watchdog.

Instead the system should stop the watchdog during the shutdown to get the
benefit of an hardware reset in case of an software related problem. This stop
can be done quite easily with procd because it keeps track of its started
processes.

Signed-off-by: Sven Eckelmann <sven.eckelmann@open-mesh.com>

SVN-Revision: 48889