Use buildroot in favor of debootstrap

[0xricksanchez]

For example, adapt the one syzkaller uses for our use case

[0xricksanchez]

Needs re-evaluating:

syzkaller uses buildroot because fuzzing wants minimal, reproducible, easily cross-compiled images to run syz-executor. Our use case is the opposite as we strive for an interactive exploit-dev where we want a fat guest in the box, debootstrap gives us that.
A buildroot image is minimal-by-design, so adding a tool means editing a buildroot config and rebuilding, not apt install.

That said buildroot would allow us to:

• Easily target cross-arch rootfs builds without binfmt pain
• Mandatory if we add fuzzing support via syzkaller