Fix test.py and tests to use an explicit --packages flag.

tests/standalone/io/test_runner_test.dart

 // Copyright (c) 2013, 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 "dart:io";
 import "dart:isolate";
 import "dart:async";
 import "../../../tools/testing/dart/test_runner.dart";
 import "../../../tools/testing/dart/test_suite.dart";
 import "../../../tools/testing/dart/test_progress.dart" as progress;
@@ skipping 123 matching lines @@
       [new EventListener()], TestController.finished);
 }
 
 class EventListener extends progress.EventListener{
   void done(TestCase test) {
     TestController.processCompletedTest(test);
   }
 }
 
 void main(List<String> arguments) {
+  // This script is in [sdk]/tests/standalone/io.
+  TestUtils.setDartDirUri(Platform.script.resolve('../../..'));
   // Run the test_runner_test if there are no command-line options.
   // Otherwise, run one of the component tests that always pass,
   // fail, or timeout.
   if (arguments.isEmpty) {
     testProcessQueue();
   } else {
     switch (arguments[0]) {
       case 'pass':
         return;
       case 'fail-unexpected':
       case 'fail':
         throw "This test always fails, to test the test scripts.";
         break;
       case 'timeout':
         // This process should be killed by the test after DEFAULT_TIMEOUT
         new Timer(new Duration(hours: 42), (){ });
         break;
       default:
         throw "Unknown option ${arguments[0]} passed to test_runner_test";
     }
   }
 }