Do not pregenerate update payloads in parallel.

bin/cros_au_test_harness.py

 #!/usr/bin/python
 
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """This module runs a suite of Auto Update tests.
 
   The tests can be run on either a virtual machine or actual device depending
   on parameters given.  Specific tests can be run by invoking --test_prefix.
@@ skipping 893 matching lines @@
   """Runs the tests given by the options and test_class in parallel."""
   threads = []
   args = []
   test_suite = _PrepareTestSuite(parser, options, test_class)
   for test in test_suite:
     test_name = test.id()
     test_case = unittest.TestLoader().loadTestsFromName(test_name)
     threads.append(unittest.TextTestRunner().run)
     args.append(test_case)
 
-  results = _RunParallelJobs(options.jobs, threads, args, print_status=False)
+  # TODO(sosa): Set back to options.jobs once parallel generation is
+  # no longer flaky.
+  results = _RunParallelJobs(1, threads, args, print_status=False)
   for test_result in results:
     if not test_result.wasSuccessful():
       Die('Test harness was not successful')
 
 
 def main():
   parser = optparse.OptionParser()
   parser.add_option('-b', '--base_image',
                     help='path to the base image.')
   parser.add_option('-r', '--board',
@@ skipping 43 matching lines @@
   else:
     dev_server_cache = None
     test_suite = _PrepareTestSuite(parser, options, test_class)
     test_result = unittest.TextTestRunner(verbosity=2).run(test_suite)
     if not test_result.wasSuccessful():
       Die('Test harness was not successful.')
 
 
 if __name__ == '__main__':
   main()