Report all swarming and isolate fatal errors in a consistent way.

tests/run_isolated_smoke_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import hashlib
 import json
 import logging
 import os
 import shutil
@@ skipping 169 matching lines @@
 
   def test_fail_empty_isolated(self):
     result_hash = self._store_result({})
     expected = [
       'state.json',
       result_hash,
     ]
     out, err, returncode = self._run(self._generate_args_with_hash(result_hash))
     if not VERBOSE:
       self.assertEqual('', out)
-      self.assertEqual('No command to run\n', err)
+      self.assertIn('No command to run\n', err)
     self.assertEqual(1, returncode)
     actual = list_files_tree(self.cache)
     self.assertEqual(sorted(expected), actual)
 
   def test_includes(self):
     # Loads an .isolated that includes another one.
 
     # References manifest2.isolated and repeated_files.isolated. Maps file3.txt
     # as file2.txt.
     result_hash = self._store('check_files.isolated')
@@ skipping 68 matching lines @@
     self.assertEqual(0, returncode)
 
     self.assertEqual(os.stat(os.path.join(self.data_dir, 'file1.txt')).st_size,
                      os.stat(cached_file_path).st_size)
 
 
 if __name__ == '__main__':
   VERBOSE = '-v' in sys.argv
   logging.basicConfig(level=logging.DEBUG if VERBOSE else logging.ERROR)
   unittest.main()