block: qemu-iotests - add vhdx log replay tests for qemu-img

VHDX logs can now be replayed via 'qemu-img check -r all'.  Add
tests to verify that the log replay is successful when using qemu-img.

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