Spec out high level behaviors for cookbook change detection

So far this is just a bunch of unimplemented tests describing the desired behavior. Agree with these? Am I missing any important cases? @opscode/client-engineers 
For checking the policyfiles we can have a hash of the bits of the policyfile which can affect the dep resolution and compare if that hash is changed during the validation. But agreed to address is later separately. 

Can't think of any other test case really other than these. :+1: