Add method to hard-kill vm, without any quit commands.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Message-Id: <20200217150246.29180-19-vsementsov@virtuozzo.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>