block: vhdx - update _make_test_img() to filter out vhdx options

The non-global option output is suppresed in _make_test_img() for
output verification in the 0?? tests.  This adds suppression for
the vhdx-unique options as well.  This allows check -vhdx to run
successfully.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
