At least --disk-size doesn't seem to be used in vyos-build. There is also no pendant for this that can be referenced via build-flavor config. If I didn't overlook anything, consider either removing the parameter or restore it's functionality.

The flavor config image_opts (https://github.com/vyos/vyos-build/blob/4c0a57920573ffe1c5d9bfbf5a01bd847a4b8e0b/scripts/image-build/build-vyos-image#L745) name-clashes with qemu-img convert native --image-opts (https://qemu-project.gitlab.io/qemu/tools/qemu-img.html#cmdoption-qemu-img-common-opts-image-opts), causing confusion when trying to understand what exactly it is supposed to do. I'd rename the parameter to reflect it is simply additional parameters for the conversion command (with all the caveats coming with the current usage, e.g. --image-opts being mutually exclusive with the hard coded usage of -f).

I can have a look at both raised points, I'd just like to discuss what implication these changes would have (or if I missed anything important regarding these parameters), before providing a PR.

Best regards