need empty-zones-enable no; in named.conf

For sites that would like to forward to their own DNS servers, the site table includes the 'forwarders' attribute to allow for this. If the site internal DNS resolves RFC1918 addresses, xCAT dns doesn't work. The reason is that empty-zones-enable in BIND defaults to yes, which creates by default empty reverse zones for all rfc1918 address blocks.

Please allow for a site option to add empty-zones-enable no; to options {} in named.conf for xCAT master node.