QA: Minor tweaks to how we check toast notifications

A toast autohides within 5 seconds and its display properties are
inherited from #mw-notification-area. This slight tweak waits for
mw-notification-area to be visible before verifying toast and its
contents

Change-Id: I89beaf9d131155e958cc9aae84a9e30ffd8e9e4f

tests/browser/features/step_definitions/common_article_steps.rb

@@ -27,7 +27,9 @@ When(/^I click the watch star$/) do
 end
 
 Then(/^I should see a toast notification$/) do
-  expect(on(ArticlePage).toast_element.when_present(10)).to be_visible
+  # To avoid flakey tests check the notification area element first (T170890)
+  expect(on(ArticlePage).notification_area_element.when_visible).to be_visible
+  expect(on(ArticlePage).toast_element.when_visible).to be_visible
 end
 
 Then(/^I should see a toast with message "(.+)"$/) do |msg|

tests/browser/features/support/pages/article_page.rb

@@ -144,6 +144,7 @@ class ArticlePage
   div(:spinner_loading, class: 'spinner loading')
 
   # toast
+  div(:notification_area, id: 'mw-notification-area')
   div(:toast, class: 'mw-notification')
 
   # loader