Re-land "Modify annotated_run to read factory configs from the slave checkout."

scripts/tools/dump_master_cfg.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """
 Dumps master config as JSON.
 
 Uses master_cfg_utils.LoadConfig, which should be called at most once
 in the same process. That's why this is a separate utility.
 """
 
 import argparse
 import json
 import os
 import sys
 
+SCRIPTS_DIR = os.path.abspath(
+    os.path.join(os.path.dirname(__file__), os.pardir))
+if not SCRIPTS_DIR in sys.path:
+  sys.path.insert(0, SCRIPTS_DIR)
+
+from common import env
+
+env.Install()
+
 from common import master_cfg_utils
 from master.factory.build_factory import BuildFactory
 
 
 class BuildbotJSONEncoder(json.JSONEncoder):
   def default(self, obj):  # pylint: disable=E0202
     if isinstance(obj, BuildFactory):
       return {'repr': repr(obj), 'properties': obj.properties.asDict()}
 
     return repr(obj)
 
 
 def main(argv):
   parser = argparse.ArgumentParser()
   parser.add_argument('master')
   parser.add_argument('output', type=argparse.FileType('w'), default=sys.stdout)
 
   args = parser.parse_args(argv)
 
   result = master_cfg_utils.LoadConfig(args.master)
   json.dump(result['BuildmasterConfig'],
             args.output,
             cls=BuildbotJSONEncoder,
             indent=4)
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))