Fix waiting for ember to be ready before running the spec

spec/acceptance_steps/users/authentication_steps.rb

@@ -67,7 +67,7 @@ step 'there is another signed in user user' do
 end
 
 step "the user should be redirected to the homepage" do
-  ember_route_should_be '/'
+  when_ember_is_ready { ember_route_should_be '/' }
 end
 
 step "the newly created user info should be stored in the local storage" do