Let bot_update recipe api force usage of bot_update.

scripts/slave/recipe_modules/bot_update/test_api.py

Index: scripts/slave/recipe_modules/bot_update/test_api.py
diff --git a/scripts/slave/recipe_modules/bot_update/test_api.py b/scripts/slave/recipe_modules/bot_update/test_api.py
index f89769b56ce3cd09a48dc6d8aedd69db5d8f0488..39a7b806fadbd4e1c172e55e7cbd22be73c51483 100644
--- a/scripts/slave/recipe_modules/bot_update/test_api.py
+++ b/scripts/slave/recipe_modules/bot_update/test_api.py
@@ -11,15 +11,17 @@ 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: