config: Look up hostnames in a defined order

Current practice is to let getaddrinfo() decide which address we get
but this is not necessarily deterministic as DNS servers won't
always return addresses in the same order if a node has
several. While this doesn't deal with node names that have
multiple IP addresses of the same family (that's an installation issue
IMHO) we can, at least, force a definite order for IPv6/IPv4 name
resolution.

I've chosen IPv6 then IPv4 as that's what happens on my test system (
using /etc/hosts) and it also seems more 'future proof'.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>