Move all tests using dart:io to a separate directory

tests/standalone/src/ProcessInvalidArgumentsTest.dart

-// Copyright (c) 2011, 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.
-//
-// Process test program to test that invalid arguments throw exceptions.
-
-#import("dart:io");
-
-void main() {
-  Expect.throws(() => new Process.start(["true"], []),
-                (e) => e is ProcessException);
-  Expect.throws(() => new Process.start("true", "asdf"),
-                (e) => e is ProcessException);
-  Expect.throws(() => new Process.start("true", ["asdf", 1]),
-                (e) => e is ProcessException);
-}