Changes to make zookeeper installation work with Kafka cluster.

The current `bcpc-hadoop` ZK installation only works with hadoop setup. Since `kafka-cookbook` community cookbook that is used within `chef-bcpc` project doesn't support ZK and `bcpc-hadoop` zookeeper recipes are very well tested, I am proposing/breaking out ZK recipes into multiple recipes. The new set of recipes include:
- attribute file `zookeeper.rb` - To define zookeeper specific attributes
- recipe `hdp_repo.rb` - To get the Hortonworks repository configured for downloading zookeeper software
- recipe `zookeeper_config.rb` - To setup zookeeper configuration files
This makes ZK recipes an independent component that can be used to setup a completely separate cluster that can be used with Kafka. 
As you pointed out in code review; this `case` statement can too go away.