meta-facebook: watchdog: Add restart cause command

Added restart cause command after taking watchdog action. This
will update dbus status for restart cause of host.

(From meta-facebook rev: 6a85046dcc41024e52ffe4a5a8678548c54ee38b)

Change-Id: I057a441a26310f80837a8fe742b669b69cf3d26e
Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>