Make cookbook more sexy

Changelog:

  * {Gemfile,Berksfile}.lock files checked in
  * metadata.rb
    * describe recipes, attributes and provided resources
  * Small improvements in recipes
    * supermarket user created with /bin/false shell instead of bash
    * nginx is enabled and started by default
    * nginx will reload configuration on change instead of restart
    * small fix to remove runtime warning about resource cloning
  * ChefSpec test added
    * correctly initialize chef-zero and upload data bag
    * check compilation
  * Integration tests
    * converted to serverspec
    * more specs: app, apt, nginx, node.js, postgres, redis and ruby