Currently, we require 0.6.2 which is just ancient. While we do some
checks and export only those functions for which libvirt counter-part
exist, 0.6.2 is just too old. Moreover, not all functions are wrapped
by libvirt version check (e.g. libvirt_connect_get_all_domain_stats).
Require 1.2.8 at least which is supposed to have all the functions
already.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>