Fix stage test_that_verifies_nav_menu_tabs and Prod test_clicking_on_con...

...tent_rating

Test failures: STAGE http://selenium.qa.mtv2.mozilla.com:8080/view/Marketplace/job/marketplace.stage.saucelabs/1774/HTML_Report/

PROD: http://selenium.qa.mtv2.mozilla.com:8080/view/Marketplace/job/marketplace.prod/1591/HTML_Report/