Parse get_subjects reponse body

Closes #28

+ Include MultiJson as a dependency
+ Bypass Zookeeper setup if ZK_URL is already defined
that echo ruok | nc doesn't work on my version of netcat (netcat-openbsd), http://stackoverflow.com/questions/21846617/why-pipeline-content-to-command-nc-wont-work. 

I assume this will work in a docker container but may not work on systems that haven't got the traditional version of netcat installed.