code: function (htmlCssSelector, attributeName) {
  
          // get the element from the page
          return driver.findElement(by.css(htmlCssSelector)).then(function(el) {
              return el.getAttribute(attributeName);
          });
      }
docs: returns the value of an attribute on an element
  @param {string} htmlCssSelector - HTML css selector used to find the element
  @param {string} attributeName - attribute name to retrieve
  @returns {string} the value of the attribute or empty string if not found
  @example
  helpers.getAttributeValue('body', 'class');