Switch to cipd module in depot_tools

scripts/slave/cipd_bootstrap.py

 # Copyright 2015 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 argparse
 import errno
 import hashlib
 import json
 import os
 import sys
@@ skipping 190 matching lines @@
                                                 package, version)
     result = {
       'executable': exe_path,
       'instance_id': instance_id
     }
     if opts.json_output:
       with open(opts.json_output, 'w') as f:
         json.dump(result, f)
   except Exception as e:
     print 'Exception installing cipd: %s' % e
-    exc_type, exc_value, exc_traceback = sys.exc_info()
+    _exc_type, _exc_value, exc_traceback = sys.exc_info()
     traceback.print_tb(exc_traceback)
     return 1
 
   return 0
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))