bot_update: make location of git cache configurable

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 123 matching lines @@
     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],
         ['--revision_mapping_file', self.m.json.input(rev_map)],
+        ['--git-cache-dir', self.m.path['git_cache']],
 
         # 3. How to find the patch, if any (issue/patchset/patch_url).
         ['--issue', issue],
         ['--patchset', patchset],
         ['--patch_url', patch_url],
         ['--rietveld_server', self.m.properties.get('rietveld')],
         ['--gerrit_repo', gerrit_repo],
         ['--gerrit_ref', gerrit_ref],
         ['--apply_issue_email_file', email_file],
         ['--apply_issue_key_file', key_file],
@@ skipping 113 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