Read got_revision_mapping from built in spec

recipe_modules/bot_update/api.py

 # 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.
 
 
 """Recipe module to ensure a checkout is consistant on a bot."""
 
 from recipe_engine import recipe_api
 
 
@@ skipping 113 matching lines @@
     # Point to the oauth2 auth files if specified.
     # These paths are where the bots put their credential files.
     if patch_oauth2:
       email_file = self.m.path['build'].join(
           'site_config', '.rietveld_client_email')
       key_file = self.m.path['build'].join(
           'site_config', '.rietveld_secret_key')
     else:
       email_file = key_file = None
 
-    rev_map = {}
-    if self.m.gclient.c:
-      rev_map = self.m.gclient.c.got_revision_mapping.as_jsonish()
+    rev_map = cfg.got_revision_mapping.as_jsonish()
 
     flags = [
         # 1. Do we want to run? (master/builder/slave).
         ['--master', master],
         ['--builder', builder],
         ['--slave', slave],
 
         # 2. What do we want to check out (spec/root/rev/rev_map).
         ['--spec', spec_string],
         ['--root', root],
@@ skipping 125 matching lines @@
 
       # bot_update actually just sets root to be the folder name of the
       # first solution.
       if step_result.json.output['did_run']:
         co_root = step_result.json.output['root']
         cwd = kwargs.get('cwd', self.m.path['slave_build'])
         if 'checkout' not in self.m.path:
           self.m.path['checkout'] = cwd.join(*co_root.split(self.m.path.sep))
 
     return step_result