DNS: check if DNS package is installed
Instead of separate checking of DNS required packages, we need just
check if IPA DNS package is installed.
https://fedorahosted.org/freeipa/ticket/4058
Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
Reviewed-By: Petr Spacek <pspacek@redhat.com>
Reviewed-By: Tomas Babej <tbabej@redhat.com>