Figure out if we can build minbase under fakechroot/fakeroot

[rsharo]

steamos_buildmach has to be run with --privileged because mkimage.sh tries to remount the proc filesystem after chrooting. We can build the fakechroot variant of SteamOS under fakeroot/fakechroot, but this eventually causes grief with systemd. Unfortunately minbase and fakechroot variants are mutually exclusive.

Would like to figure out a way to build the minbase variant as a normal user and without the --privileged flag -- without maintaining our own fork of /usr/share/debootstrap/scripts/stable.