Setting node attributes!

* using Ridley to set node attributes
* tests for all the things! client, app, and chef_interface
* changed method asserting endpoint required params to handle the failure, as well as be a little more ruby-ish. Hooray for star-args (*like_this) and their auto-expansion into arrays!
* added Proc-based exception handling method for client REST calls 

Following the merge to master, I will deploy these changes to our production box.

:penguin: