Merge pull request #58 from SUSE-Cloud/release/pebbles/master

https://github.com/crowbar/barclamp-dns/pull/58

Merged by devtool for ArkadyKanevsky
use forward only option

- this is needed to resolve reverse DNS for external private IPs
  because bind 9.9 defaults to empty-zones-enable yes
- this allows to better run behind firewalls