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

pkg/analysis_server/test/integration/integration_tests.dart

 // Copyright (c) 2014, 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.
 
 library test.integration.analysis;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:io';
@@ skipping 618 matching lines @@
       } else {
         arguments.add('--observe=$servicesPort');
       }
       arguments.add('--pause-isolates-on-exit');
     } else if (servicesPort != null) {
       arguments.add('--enable-vm-service=$servicesPort');
     }
     if (Platform.packageRoot != null) {
       arguments.add('--package-root=${Platform.packageRoot}');
     }
+    if (Platform.packageConfig != null) {
+      arguments.add('--packages=${Platform.packageConfig}');
+    }
     if (checked) {
       arguments.add('--checked');
     }
     //
     // Add the server executable.
     //
     arguments.add(serverPath);
     //
     // Add server arguments.
     //
@@ skipping 268 matching lines @@
   void populateMismatches(item, List<MismatchDescriber> mismatches);
 
   /**
    * Create a [MismatchDescriber] describing a mismatch with a simple string.
    */
   MismatchDescriber simpleDescription(String description) =>
       (Description mismatchDescription) {
         mismatchDescription.add(description);
       };
 }