libcli/dns: Add resolv.conf parsing

libcli/dns: Add resolv.conf parsing

Right now this only looks at the nameserver setting. It is initally made for
asynchronous AD DC lookup routines, where we don't need the "search", "domain"
and other settings. When we convert general "net", "smbclient" and others to
use this, we might either add "domain" handling to this code or look at
something like c-ares which already does it.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>