Split secure_server_client_certificate test in two, because of session cache.

tests/standalone/io/secure_server_client_no_certificate_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:async";
+import "dart:io";
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+import "package:path/path.dart";
+
+const HOST_NAME = "localhost";
+const CERTIFICATE = "localhost_cert";
+
+Future testNoClientCertificate() {
+  var completer = new Completer();
+  SecureServerSocket.bind(HOST_NAME,
+                          0,
+                          CERTIFICATE,
+                          requestClientCertificate: true).then((server) {
+    var clientEndFuture = SecureSocket.connect(HOST_NAME,
+                                               server.port);
+    server.listen((serverEnd) {
+      X509Certificate certificate = serverEnd.peerCertificate;
+      Expect.isNull(certificate);
+      clientEndFuture.then((clientEnd) {
+        clientEnd.close();
+        serverEnd.close();
+        server.close();
+        completer.complete();
+      });
+    });
+  });
+  return completer.future;
+}
+
+Future testNoRequiredClientCertificate() {
+  var completer = new Completer();
+  bool clientError = false;
+  SecureServerSocket.bind(HOST_NAME,
+                          0,
+                          CERTIFICATE,
+                          requireClientCertificate: true).then((server) {
+    Future clientDone = SecureSocket.connect(HOST_NAME, server.port)
+      .catchError((e) { clientError = true; });
+    server.listen((serverEnd) {
+      Expect.fail("Got a unverifiable connection");
+    },
+    onError: (e) {
+      clientDone.then((_) {
+        Expect.isTrue(clientError);
+        server.close();
+        completer.complete();
+      });
+    });
+  });
+  return completer.future;
+}
+
+void main() {
+  String certificateDatabase = join(dirname(Platform.script), 'pkcert');
+  SecureSocket.initialize(database: certificateDatabase,
+                          password: 'dartdart',
+                          useBuiltinRoots: false);
+
+  asyncStart();
+  testNoRequiredClientCertificate()
+    .then((_) => testNoClientCertificate())
+    .then((_) => asyncEnd());
+}