mkosi for test image builds

[Torxed]

It's significantly faster than mkarchiso, and produce smaller images in general.
The downside might be that mkosi use case is probably not this.

The current limiting factor is that I have no idea how to get mkosi to boot the disk image after archinstall has done it's thing. But using this to test installs works fine if done with:

mkosi -B build
mkosi qemu \
  --drive=archinstall_small:25G \
  -- \
  -device nvme,serial=archinstall_small,drive=archinstall_small

You could manually craft a qemu-system-x86_64 command line, but the whole point of swapping to mkosi would be that it would allow us to do:

mkosi build -B
mkosi qemu

And both build with the latest/given archinstall, and also facilitate a qemu "builder" that matches whatever we built.

Currently exploring ways of booting the archinstall'd system: Torxed/mkosi@6f3c208

[svartkanin]

Looking forward to it, the current build step is slooooooooowwww