Comment 2 for bug 565380

This is the error in question:
Setting up libvirt-bin (0.7.5-5ubuntu25) ...
Installing new version of config file /etc/apparmor.d/usr.lib.libvirt.virt-aa-helper ...
adduser: The user `tester' does not exist.
dpkg: error processing libvirt-bin (--configure):
 subprocess installed post-installation script returned error exit status 1
Setting up python-libvirt (0.7.5-5ubuntu25) ...

This must be caused by the following snippet in libvirt-bin.postinst:
        # Add each admin user to the libvirtd group
        for u in $(grep "^admin:" /etc/group | sed -e "s/^.*://" -e "s/,/ /g"); do
                adduser "$u" libvirtd >/dev/null
        done

It seems you have a 'tester' user that you removed from the system, but forgot to remove from the 'admin' group. Please adjust your /etc/group file accordingly. Then you can run 'sudo apt-get -f install ; sudo apt-get upgrade' to cleanup.

The postinst should probably be adjusted to have:
  adduser "$u" libvirtd >/dev/null || true