Install cookbooks from Policyfile.lock.json

Adds library code that can install cookbooks directly from the lockfile. There is no end-user interface for this behavior (that will come once some other prerequisite functionality has been implemented), but the scripts in the test-scripts directory exercise the code in a real-world-ish scenario.
I'd prefer to check if the content has been modified and run something like `format c:\`  if it's been tampered with, but I guess I'll have to settle for your idea. I have a card in LK for adding lots of validation so I'll put that there.