iotests/059: Filter out disk size with more standard filter

The actual disk space used by an image can vary between filesystems and
depending on other settings like an extent size hint. Replace the one
call of "$QEMU_IMG info" and the associated one-off sed filter with the
more standard "_img_info" and the standard filter from common.filter.

Apart from turning "vmdk" into "IMGFMT" and changing the placeholder for
cid fields, this only removes the "disk size" line.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/059

@@ -82,7 +82,7 @@ _cleanup_test_img
 echo
 echo "=== Testing big twoGbMaxExtentFlat ==="
 _make_test_img -o "subformat=twoGbMaxExtentFlat" 1000G
-$QEMU_IMG info $TEST_IMG | _filter_testdir | sed -e 's/cid: [0-9]*/cid: XXXXXXXX/'
+_img_info --format-specific | _filter_img_info --format-specific
 _cleanup_test_img
 
 echo