docs: def metadata(self):
          """Return dict representation of this cookbook's metadata.rb ."""
          self.metadata_path = os.path.join(self.path, 'metadata.rb')
          if not os.path.isfile(self.metadata_path):
              raise ValueError("Cookbook needs metadata.rb, %s"
                               % self.metadata_path)
  
          if not self._metadata:
              self._metadata = MetadataRb(open(self.metadata_path, 'r+'))
  
          return self._metadata