Support for debian images

I have been able to make debian images work in MAAS[0] but changes in MAAS 3.1 now require all images to have a supported base image. Since debian is not a supported image, any debian images I’ve uploaded will stop working. Previously uploaded images fail with the cryptic:

not enough values to unpack (expected 2, got 1)

And uploading new images fail with:

{"base_image": ["custom images require a valid base image name"]}

or, if you supply base_image=debian/buster you get:

{"base_image": ["custom images require a valid non-custom OS type base image"]}

We haven’t required official support debian images in the past but with the update to 3.1, it becomes critical.

[0] I’ve successfully built debian images using info gleaned from this discourse such as this post as well as other sources such as askubuntu.