use libguestfs API to inspect GPT images
Submitted by Federico Bruni
Please see this discussion: https://github.com/systemd/mkosi/issues/197
Boxes currently uses libosinfo to detect the OS of ISO files. It would be nice if it was able to detect the OS of other kind of images, such as GPT images.
In above discussion it was suggested to use libguestfs APIs to inspect the disk image.