DNS server upgrade: do not fail when DNS server did not respond
Previously, update_dnsforward_emptyzones failed with an exeception if
DNS query failed for some reason. Now the error is logged and upgrade
I assume that this is okay because the DNS query is used as heuristics
of last resort in the upgrade logic and failure to do so should not have
catastrophics consequences: In the worst case, the admin needs to
manually change forwarding policy from 'first' to 'only'.
In the end I have decided not to auto-start BIND because BIND depends on
GSSAPI for authentication, which in turn depends on KDC ... Alternative
like reconfiguring BIND to use LDAPI+EXTERNAL and reconfiguring DS to
accept LDAP external bind from named user are too complicated.
Reviewed-By: Martin Basti <firstname.lastname@example.org>