mdmon: suicide prevention

mdmon: suicide prevention

mdmon cannot remove the pidfile at shutdown becuase it needs to stay
running across the "mount -o remount,ro /" event.  When it relaunches
after a reboot there is a good chance that the pid will match what was
there previously.  The result is that the "take over for unresponsive
mdmon" logic results in self termination.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>