use node.default to be more respectful of users

Using node.set has several problems:

  * It stores the data on the chef server (and we use node.set for apikeys. Bad!)
  * It means the user has to at least set a normal attribute on their node/role/env
Merge pull request #38 from racker/jordane/dont_set_normal_attributes

use node.default to be more respectful of users