puppet: introduce hiera for production

* Introduce the hieradata dir in the puppet repo
* Install hiera.yaml in production
* Link hieradata dir in /etc/puppet/hiera

After this change is merged, we can start using hiera actively.

Change-Id: I8bd23ba3163b427ff1fd337188fbd28eaad44d3e
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>