Add ability for cbuildbot master to synchronize with cbuildbot slaves.

bin/cbuildbot_config.py

-#!/usr/bin/python
-
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# Dictionary values that aren't self-explanatory:
+# 'master' - only one allowed to be True.  This bot controls the uprev process.
+# 'important' - master bot uses important bots to determine overall status.
+#               i.e. if master bot succeeds and other important slaves succeed
+#               then the master will uprev packages.  This should align
+#               with info vs. closer except for the master.
+# 'hostname' - Needed for 'important' slaves.  The hostname of the bot.  Should
+#              match hostname in slaves.cfg in buildbot checkout.
+
 config = {}
 config['default'] = {
   'board' : 'x86-generic',
   'uprev' : False,
+  'master' : False,
+  'important' : False,
 }
 config['x86-generic-pre-flight-queue'] = {
   'board' : 'x86-generic',
   'uprev' : True,
+  'master' : True,
+  'important' : False,
 }