block: qemu-iotests for vhdx, add write test support

This removes the IMGFMT_GENERIC blocker for read-only, so existing
iotests run read/write tests for vhdx images created by qemu-img (e.g.
tests 001, 002, 003).

In addition, this updates the sample image test for the Hyper-V
created image, to verify we can write it as well.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/tests/qemu-iotests/064 b/tests/qemu-iotests/064
index 6789aa6..1c74c31 100755
--- a/tests/qemu-iotests/064
+++ b/tests/qemu-iotests/064
@@ -56,6 +56,17 @@
 echo "=== Verify pattern 0x00, 66M - 1024M ==="
 $QEMU_IO -r -c "read -pP 0x00 66M 958M" "$TEST_IMG" | _filter_qemu_io
 
+echo
+echo "=== Verify pattern write, 0xc3 99M-157M ==="
+$QEMU_IO -c "write -pP 0xc3 99M 58M" "$TEST_IMG" | _filter_qemu_io
+# first verify we didn't write where we should not have
+$QEMU_IO -c "read -pP 0xa5 0 33M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "read -pP 0x96 33M 33M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "read -pP 0x00 66M 33M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "read -pP 0x00 157MM 867MM" "$TEST_IMG" | _filter_qemu_io
+# now verify what we should have actually written
+$QEMU_IO -c "read -pP 0xc3 99M 58M" "$TEST_IMG" | _filter_qemu_io
+
 # success, all done
 echo "*** done"
 rm -f $seq.full