Remove thirdparty/unittest2 from webkitpy and require python2.7.

Tools/Scripts/webkitpy/common/system/executive.py

 # Copyright (c) 2009, Google Inc. All rights reserved.
 # Copyright (c) 2009 Apple Inc. All rights reserved.
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 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
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 # this software without specific prior written permission.
 #
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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+import StringIO
 import errno
 import logging
 import multiprocessing
 import os
-import StringIO
 import signal
 import subprocess
 import sys
 import time
 
 from webkitpy.common.system.outputtee import Tee
 from webkitpy.common.system.filesystem import FileSystem
 
 
 _log = logging.getLogger(__name__)
@@ skipping 435 matching lines @@
         pool.join()
         return results
 
 
 def _run_command_thunk(cmd_line_and_cwd):
     # Note that this needs to be a bare module (and hence Picklable) method to work with multiprocessing.Pool.
     (cmd_line, cwd) = cmd_line_and_cwd
     proc = subprocess.Popen(cmd_line, cwd=cwd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
     stdout, stderr = proc.communicate()
     return (proc.returncode, stdout, stderr)