qemu-iotests: update unsupported image formats in 194

Test 194 checks for 'luks' to exclude as an unsupported format,
However, most formats are unsupported, due to migration blockers.

Rather than specifying a blacklist of unsupported formats, whitelist
supported formats (specifically, qcow2, qed, raw, dmg).

Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Message-id: 23ca18c7f843c86a28b1529ca9ac6db4b35ca0e4.1510059970.git.jcody@redhat.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Max Reitz <mreitz@redhat.com>

Author: codyprime

tests/qemu-iotests/194

@@ -21,7 +21,7 @@
 
 import iotests
 
-iotests.verify_image_format(unsupported_fmts=['luks'])
+iotests.verify_image_format(supported_fmts=['qcow2', 'qed', 'raw', 'dmg'])
 iotests.verify_platform(['linux'])
 
 with iotests.FilePath('source.img') as source_img_path, \