test.pl: Harden watchdog against glitches

Only one type of watchdog timer supposedly can exist. But I can see the possibility that a temporary glitch in the system caused a fallback type to be used. This commit simply makes sure that when cancelling, anything out there gets cancelled, instead of assuming there's just one possibility.

Author: khwilliamson

t/test.pl

@@ -1851,11 +1851,11 @@ ($;$)
  $watchdog_thread->kill('KILL');
  undef $watchdog_thread;
  }
- elsif ($watchdog_process) {
+ if ($watchdog_process) {
  kill('KILL', $watchdog_process);
  undef $watchdog_process;
  }
- elsif ($watchdog_alarm) {
+ if ($watchdog_alarm) {
  alarm(0);
  undef $watchdog_alarm;
  }