[COOKBOOKS] Added versioned_cookbooks support.

 - Adding "versioned_cookbooks true" to knife.rb turns on versioned cookbook mode
 - Cookbooks are assumed to be named such as:

cookbooks/
  apt-1.8.4
  apt-1.7.0
  postgresql-2.2.2

 - This allows for multiple versions.
 - Caveat: this commit requires the CHEF-3307 patch against chef 10-stable
[GEM] Added Gemfile for testing