tests: fix broken tests.

* Fix a broken Twitter profile image upload test.
* Skip a broken DeviantArt flash file upload test (flash no longer
  supported by DeviantArt?)
* Skip user upgrade tests when Stripe is not configured.

test/functional/user_upgrades_controller_test.rb

@@ -2,6 +2,10 @@ require 'test_helper'
 
 class UserUpgradesControllerTest < ActionDispatch::IntegrationTest
   context "The user upgrades controller" do
+    setup do
+      skip unless UserUpgrade.enabled?
+    end
+
     context "new action" do
       should "render for a self upgrade to Gold" do
         @user = create(:user)