Add a watchdog timer for ShutDownAndCore(PANIC)

Add a watchdog timer for ShutDownAndCore(PANIC)

Add a watchdog timer that is started when ShutDownAndCore(PANIC) is
called, to ensure we actually panic and do not e.g. get stuck in
deadlock.

Change-Id: I9201fe7d09aeb6819beefaf1755b51129c7bda6b
Reviewed-on: http://gerrit.openafs.org/873
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>