Bug#812584: Support lxc-based build environment

[Yuri D'Elia]

Package: pbuilder
Version: 0.222
Severity: wishlist

lxc-based containers with an overlay image would be a superior replacement to
chroot-based images, and would make cowbuilder basically obsolete.

In fact, autopkgtest has support for lxc containers as well, and it would be
nice if we could share (in one way or the other) the same base container for
both building and testing a package.