Support testing flatpak infos, we do it by faking /.flatpak-info file in case we're building in test mode.
Classic snaps are just a kind of packages with no sandbox at all, so there's no point to mark them as sandboxed. In this way we can just do IO checks once without having to multiply them. Co-Authored-by: Robert Ancell <robert.ancell@canonical.com>
So we don't have to bother to manually remove the created artifacts.
