build process should work inside containers

[jmtd]

I'm surprised this didn't occur to me earlier, but we should generally run the builds inside containers themselves, so the host does not need to be Debian/have debootstrap around. There is one edge-case for bootstrapping, obviously you need an image to spawn builder containers from, but once you've got one, that's the exception rather than the rule.

[orent]

I tried something similar but the bootstrapping to run everything inside the container was ugly.

Eventually i found a simpler solution: run fakeroot debootstrap --foreign on the host, and so the debootstrap --second-stage inside the container.

Debootstrap --foreign has very few dependencies and can be made to run on non-debian hosts without much trouble.