Merge v1.4.1 + Ubuntu group fix

Hi, this updates us to the recent version 1.4.1 Ubuntu has a delta that - by the virtue of different policykit/permission handling - isn't needed by Debian. But it would help a lot to get it accepted and via dpkg-vendor --derives-from Ubuntu we can do so while keeping it a no-op for you.

dpkg-vendor is usually always present since we have debhelper-compat=12 => debhelper => dpkg-dev. Let me know if you'd want to see that expressed as an explicit depends in d/control

Attached is a build log in unstable amd64: libvirt-dbus_1.4.1-1_amd64.build