By default, o2cb fences the box by calling emergency_restart(). While this
scheme works well in production, it comes in the way during testing as it
does not let the tester take stack/core dumps for analysis.

This patch allows user to dynamically change the fence method to panic() by:
# echo "panic" > /sys/kernel/config/cluster/<clustername>/fence_method
Signed-off-by: NSunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>