Fix config file error for CentOS and RHEL variants

Fix a couple of issues in a RHEL variant. Tested on CentOS 6.4.

- Now it overrides the config_file `named.conf` on a RHEL variant so that the options_file `named.conf.options` and local_files `named.conf.lecal` are no longer ignored.
- The zone files are now placed under the data_path.
- Set a SELinux attribute to avoid errors when dynamic DNS is enabled.

Note that this pull request also contains the changes from the following pull requests:

- #2 "Support SmartOS, lists in attributes" by @wohali
- #7 "Added support for DDNS keys" by @cdoughty77