Refactor service tests in preparation of running on sky_shell

runtime/observatory/tests/service/capture_stdio_test.dart

 // Copyright (c) 2015, 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.
 // VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
 
 import 'dart:async';
 import 'dart:developer';
 import 'dart:io';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
+import 'service_test_common.dart';
 import 'test_helper.dart';
 
 void test() {
   debugger();
   stdout.write('stdout');
 
   debugger();
   print('print');
 
   debugger();
@@ skipping 59 matching lines @@
           completer.complete();
         });
       });
     await isolate.resume();
     await completer.future;
   },
 ];
 
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: test);