code: function(imageIdentifier, callback) {
          request.get(this.getMetadataUrl(imageIdentifier), function(err, res, body) {
              callback(err, body, res);
          });
  
          return this;
      }
docs: Get metadata attached to an image
  
  @param {String}   imageIdentifier
  @param {Function} callback
  @return {ImboClient}