Don't quit debugger when the program terminates, only after `quit`.

tests/cli_tests/interactive_debugger_tests.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.
 
 import 'dart:async' show
     Future,
     StreamIterator;
 
 import 'dart:convert' show
     LineSplitter,
@@ skipping 226 matching lines @@
 });
 
 Test listProcesses = new Test("debugger_list_processes",
     (InteractiveDebuggerTestContext context) async {
   await context.runCommandAndExpectPrompt("b resumeChild");
   await context.runCommandAndExpectPrompt("r");
   await context.runCommandAndExpectPrompt("lp");
   await context.runCommandAndExpectPrompt("c");
   await context.runCommandAndExpectPrompt("lp");
   await context.runCommandAndExpectPrompt("c");
-  await context.expectExitCode(0);
+  await context.quitWithoutError();
 });
 
 Test relativePath = new Test("debugger_relative_file_reference",
     (InteractiveDebuggerTestContext context) async {
   await context.runCommandAndExpectPrompt("bf ${context.test.filePath} 13");
   await context.expectOut(
       "### set breakpoint id: '0' method: 'main' bytecode index: '0'");
   await context.runCommandAndExpectPrompt("r");
   await context.quitWithoutError();
 }, // Working directory that is not the dartino-root directory.
@@ skipping 29 matching lines @@
   await context.quitWithoutError();
 }, filepath: "debugger_trivial.dart");
 
 main(List<String> args) async {
   for (Test test in tests) {
     if (args.any((arg) => test.name.indexOf(arg) >= 0)) {
       await test.run(new BuildViaSessionTestContext());
     }
   }
 }