Emit a non-zero exit code when Pub fails.

utils/tests/pub/pub_install_git_test.dart

 // Copyright (c) 2012, 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('pub_tests');
 
 #import('dart:io');
 
 #import('test_pub.dart');
 #import('../../../pkg/unittest/unittest.dart');
@@ skipping 81 matching lines @@
           "weird-name": {"git": "../foo.git"}
         }
       })
     ]).scheduleCreate();
 
     // TODO(nweiz): clean up this RegExp when either issue 4706 or 4707 is
     // fixed.
     schedulePub(args: ['install'],
         error: const RegExp(@'^FormatException: The name you specified for '
             @'your dependency, "weird-name", doesn' @"'" @'t match the name '
-            @'"foo" \(from "\.\./foo\.git"\)\.'));
+            @'"foo" \(from "\.\./foo\.git"\)\.'),
+        exitCode: 1);
 
     run();
   });
 
   test('checks out and updates a package from Git', () {
     ensureGit();
 
     git('foo.git', [
       file('foo.dart', 'main() => "foo";')
     ]).scheduleCreate();
@@ skipping 247 matching lines @@
       dir(packagesPath, [
         dir('foo', [
           file('foo.dart', 'main() => "foo";')
         ])
       ]).scheduleValidate();
 
       run();
     });
   });
 }