I've a query about the change.
Now resizes are always done on qcow file in the instance directory.
That will introduce a possibly unexpected change when using
unpartitioned ext images, as they'll no longer have their
file system resized up (as resize2fs will fail on the qcow2 file).
Maybe we document this in release notes, that the limited
file system resizing is no longer supported?
Or perhaps we key this new behaviour on whether the
image in base could be resized (disk.can_resize_fs(_base_image, size))