Add an integration test for execution.setSubscriptions.

pkg/analysis_server/test/integration/execution/test_all.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'create_context_test.dart' as create_context_test;
 import 'delete_context_test.dart' as delete_context_test;
 import 'map_uri_test.dart' as map_uri_test;
+import 'set_subscription_test.dart' as set_subscription_test;
 
 main() {
   defineReflectiveSuite(() {
     create_context_test.main();
     delete_context_test.main();
     map_uri_test.main();
+    set_subscription_test.main();
   }, name: 'execution');
 }