Fix Ubuntu upgrade

Fetch the correct `libsbc1` packages (both on Ubuntu -le quantal and Debian wheezy).

Remove `xserver-xephyr` apt-preference on release -gt quantal (for some reason the current preference file does not work, I tried to fix it, but couldn't get it to work).

Finally, add a test framework for Ubuntu upgrade (`03_upgrade`). We could expand it later for LTS->LTS updates, as well as Debian upgrades.

Tested on all distributions (`02_audio`), as well as upgrade path precise->trusty (`03_upgrade`).