Readding xfail

Adding the xfail because https://bugzilla.mozilla.org/show_bug.cgi?id=800341 was reopened and test fails on CI 
http://qa-selenium.mv.mozilla.com:8080/view/Marketplace/job/marketplace.dev.developer_hub/lastCompletedBuild/testReport/tests.desktop.developer_hub.test_developer_hub/TestDeveloperHub/test_that_checks_editing_basic_info_for_a_free_app/