Lots of changes.

Using the Puppet hiera tool in place of a hardcoded site.pp file.
The hiera YAML files provide both node to class mappings and the necessary variables.
There is probably more I can do here to make adding more datanodes really easy.

Added templating support for the ntp_client and hadoop modules.

Renamed the hadoop-* services to a more appropriate name of hdfs-*.

Added full class subscription between hadoop::base and hadoop::*node.

Extracted any remaining templated config files from the hadoop module into empty hbase and zookeeper modules.
The implementation of these modules will be coming around soon.