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.

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>
(cherry picked from commit 9bff2027cb963343778001512d5cdf00cc7094c6)

Change-Id: If91606ff50aa19a614edf51e274d055bb8b30618
Reviewed-on: http://gerrit.openafs.org/991
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>