test-backend: Fix missing output for untested templates.

Our enforcement logic for untested templates unfortunately did not
give a clear error message unless you passed the --verbose option.

tools/test-backend

@@ -174,10 +174,9 @@ if __name__ == "__main__":
     templates_not_rendered = test_runner.get_shallow_tested_templates()
     if templates_not_rendered:
         missed_count = len(templates_not_rendered)
-        if options.verbose:
-            print("*** Shallow tested templates: {}".format(missed_count))
+        print("\nError: %s templates have no tests!".format(missed_count))
         for template in templates_not_rendered:
-                print('--- {}'.format(template))
+            print('  {}'.format(template))
         failures = True
 
     if options.coverage: