DNS: Fix realm domains integration with DNS zone add.
Realmdomains integration into DNS commands pre-dates split of DNS forward zones
and DNS master zones into two distinct commands.
There was an forgotten condition in dnszone_add command which caused omission
of DNS master zones with non-empty forwarders from realmdomain list.
https://fedorahosted.org/freeipa/ticket/5980
Reviewed-By: Martin Basti <mbasti@redhat.com>