Let bot_update recipe api force usage of bot_update.

scripts/slave/recipe_modules/bot_update/test_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.
 
 import hashlib
 import struct
 
 from slave import bot_update
 from slave import recipe_test_api
 
 
 class BotUpdateTestApi(recipe_test_api.RecipeTestApi):
   def output_json(self, master, builder, slave, root, first_sln,
-                  revision_mapping, git_mode):
+                  revision_mapping, git_mode, force=False):
     """Deterministically synthesize json.output test data for gclient's
     --output-json option.
     """
-    active = bot_update.check_valid_host(master, builder, slave)
+    active = bot_update.check_valid_host(master, builder, slave) or force
 
     output = {
         'did_run': active
     }
+    if force:  # pragma: no cover
+      output.update({'force': True})
 
     # Add in extra json output if active.
     if active:
       properties = {
           property_name: self.gen_revision(project_name, git_mode)
           for project_name, property_name in revision_mapping.iteritems()
       }
       # We also want to simulate outputting "got_revision_git": ...
       # when git mode is off to match what bot_update.py does.
       if not git_mode:
@@ skipping 11 matching lines @@
 
 
   @staticmethod
   def gen_revision(project, GIT_MODE):
     """Hash project to bogus deterministic revision values."""
     h = hashlib.sha1(project)
     if GIT_MODE:
       return h.hexdigest()
     else:
       return struct.unpack('!I', h.digest()[:4])[0] % 300000