fence_sanlock: new code
    
    A fence agent that uses /dev/watchdog to reset hosts.
    Per-host sanlock leases on shared storage are used:
    - for hosts to detect that they are being fenced by
      someone if they haven't actually failed
    - for hosts to verify that fenced hosts have been
      reset by seeing their host_id leases expire (not
      be renewed on disk)
    - for hosts to know how long to wait after fencing
      before they can proceed, based on acquiring the
      expired lease of the fenced host
    
    Signed-off-by: David Teigland <teigland@redhat.com>