iotests: 205: support luks format Support default luks options in VM.add_drive and in new library function qemu_img_create. Use it in 205 iotests. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20180206182507.21753-1-vsementsov@virtuozzo.com> Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com>