Initialize a new instance of Rails.application during integration tests

This is to fix the AWDWR tests until the application object is refactored to be a singleton.

actionpack/lib/action_dispatch/testing/integration.rb

@@ -486,7 +486,7 @@ class IntegrationTest < ActiveSupport::TestCase
     def self.app
       # DEPRECATE Rails application fallback
       # This should be set by the initializer
-      @@app || (defined?(Rails.application) && Rails.application) || nil
+      @@app || (defined?(Rails.application) && Rails.application.new) || nil
     end
 
     def self.app=(app)