Enhance login wait, remove home_page wait and skip 'purchase app' test

http://qa-selenium.mv.mozilla.com:8080/view/Marketplace/job/marketplace.prod/723/testReport/junit/tests.desktop.consumer_pages.test_users_account/TestAccounts/test_user_can_sign_in_and_sign_out_in_consumer_pages/

or 

http://qa-selenium.mv.mozilla.com:8080/view/Marketplace/job/marketplace.prod/696/testReport/

Prod is intermittently failing on _throbber_locator, we should just remove it as we already waiting for Favorite apps to appear