libvirtd.conf uses "libvirt" as the value of "unix_sock_group",
however, group "libvirt" may not exist on the system, in this case
the case will always fail.
As a solution, replace "libvirt" with "$USER" in "tmp.conf".
# Start with the sample libvirtd.conf file, uncommenting all real directives.
sed -n 's/^#\([^ #]\)/\1/p' "$conf" > tmp.conf
+sed -e "s/^\(unix_sock_group =\).*/\1 \"$USER\"/g" tmp.conf > k
+mv k tmp.conf
+
# Iterate through that list of directives, corrupting one RHS at a
# time and running libvirtd with the resulting config. Each libvirtd
# invocation must fail.