shutdown: release the watchdog finally

During reboot or kexec, watchdog will be setup before systemd is
replaced by systemd-shutdown binary. But while systemd-shutdown is
executed, the watchdog will not really be released. Log shown as
following:

[   39.371202] watchdog: watchdog0: watchdog did not stop!
[   39.383659] systemd-shutdown[1]: Syncing filesystems and block
devices.
[   39.423727] systemd-shutdown[1]: Sending SIGTERM to remaining
processes...
[   39.440857] systemd-journald[526]: Received SIGTERM from PID 1
(systemd-shutdow).
[   39.461047] systemd-shutdown[1]: Sending SIGKILL to remaining
processes...
[   39.466736] systemd-shutdown[1]: Using hardware watchdog 'iTCO_wdt',
version 0, device /dev/watchdog
[   39.467835] systemd-shutdown[1]: Unmounting file systems.
[   39.469721] [2171]: Remounting '/' read-only in with options
'attr2,inode64,logbufs=8,logbsize=32k,noquota'.
[   39.550266] systemd-shutdown[1]: All filesystems unmounted.
[   39.550274] systemd-shutdown[1]: Deactivating swaps.
[   39.550443] systemd-shutdown[1]: All swaps deactivated.
[   39.550449] systemd-shutdown[1]: Detaching loop devices.
[   39.550697] systemd-shutdown[1]: All loop devices detached.
[   39.550703] systemd-shutdown[1]: Detaching DM devices.
[   39.551269] systemd-shutdown[1]: Not all DM devices detached, 1
left.
[   39.551277] systemd-shutdown[1]: Cannot finalize remaining DM
devices, continuing.
[   39.580044] systemd-shutdown[1]: Successfully changed into root
pivot.
[   39.580050] systemd-shutdown[1]: Returning to initrd...
[   39.587921] watchdog: watchdog0: watchdog did not stop!
[   39.774130] dracut Warning: Break before pre-shutdown

after applying fix

[   59.520379] watchdog: watchdog0: watchdog did not stop!
[   59.542286] systemd-shutdown[1]: Syncing filesystems and block
devices.
[   59.583313] systemd-shutdown[1]: Sending SIGTERM to remaining
processes...
[   59.600133] systemd-journald[517]: Received SIGTERM from PID 1
(systemd-shutdow).
[   59.624435] systemd-shutdown[1]: Sending SIGKILL to remaining
processes...
[   59.629288] systemd-shutdown[1]: Using hardware watchdog
'iTCO_wdt', version 0, device /dev/watchdog
[   59.630468] systemd-shutdown[1]: Unmounting file systems.
[   59.632219] [2172]: Remounting '/' read-only in with options
'attr2,inode64,logbufs=8,logbsize=32k,noquota'.
[   59.727588] systemd-shutdown[1]: All filesystems unmounted.
[   59.727596] systemd-shutdown[1]: Deactivating swaps.
[   59.727719] systemd-shutdown[1]: All swaps deactivated.
[   59.727725] systemd-shutdown[1]: Detaching loop devices.
[   59.727974] systemd-shutdown[1]: All loop devices detached.
[   59.727979] systemd-shutdown[1]: Detaching DM devices.
[   59.728547] systemd-shutdown[1]: Not all DM devices detached, 1
left.
[   59.728556] systemd-shutdown[1]: Cannot finalize remaining DM
devices, continuing.
[   59.758160] systemd-shutdown[1]: Successfully changed into root
pivot.
[   59.758167] systemd-shutdown[1]: Returning to initrd...
[   59.950305] dracut Warning: Break before pre-shutdown

src/shutdown/shutdown.c

@@ -532,6 +532,7 @@ int main(int argc, char *argv[]) {
         }
 
         /* We're done with the watchdog. */
+        watchdog_close(true);
         watchdog_free_device();
 
         arguments[0] = NULL;