Add FreeBSD support and forward-zones

[Godwottery]

Added support for installing powedns-recursor on FreeBSD
Added support for managing forward-zones from Ansible

[pieterlexis]

Awesome, thanks for this! I have 2 suggestions so current behaviour is unmodified, along with these comments:

Can you add this to defaults/main.yml:

pdns_rec_forward_zones: []

Can you mention in the README that on FreeBSD, the repository options are not honored?

Could you add FreeBSD to the supported systems in meta/galaxy.yml?

I'm not a fan of using hashes for config options, perhaps changing pdns_fileowner to pdns_rec_file_owner and pdns_rec_file_group is cleaner.

And YAML lint is complaining:

--> Executing Yamllint on files found in /home/travis/build/PowerDNS/pdns_recursor-ansible/...
    /home/travis/build/PowerDNS/pdns_recursor-ansible/tasks/install-FreeBSD.yml
      7:1       error    too many blank lines (1 > 0)  (empty-lines)

[Godwottery]

Can you add this to defaults/main.yml:
Done

Can you mention in the README that on FreeBSD, the repository options are not honored?
Added

Could you add FreeBSD to the supported systems in meta/galaxy.yml?
Fixed in meta/main.yml, under the galaxy section. I assume that is what you meant.

I'm not a fan of using hashes for config options, perhaps changing pdns_fileowner to pdns_rec_file_owner and pdns_rec_file_group is cleaner.
See comment above

And YAML lint is complaining:
Fixed

[Godwottery]

Test failure: fatal: [centos-6]: FAILED! => {"changed": false, "msg": "Failure talking to yum: Cannot find a valid baseurl for repo: base"}
Does not seem to be causes by this PR.

[pieterlexis]

I've re-created your contribution in #64 as it diverged too much. Thanks for starting this!