Compatible with CentOS 6.

Hello Adam,

I've added CentOS 6-compatibility by placing the necessary variables in server/params.pp. Unfortunately I haven't got the time to install Ubuntu to test this branch, hopefully you can test this on Ubuntu before merging it.

To get the Bind-process include named.conf.local in CentOS, I've used the puppet-line-module (https://github.com/ahaitoute/puppet-line) to add the include named.conf.local-line entry in named.conf. I'm not sure if this can be handled by the concat-module and if this entry addition is also necessary in Ubuntu.