bot_update: remove activation check for non-masters

Cherry-pick https://codereview.chromium.org/2000403004/ to depot_tools's
bot_update.py

R=hinoka@chromium.org
BUG=613641

Review-Url: https://codereview.chromium.org/2022453003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300670 0039d316-1c4b-4281-b951-d872f2087c98

recipe_modules/bot_update/resources/bot_update.py

@@ -1457,7 +1457,9 @@ def parse_args():
   parse.add_option('--gerrit_no_reset', action='store_true',
                    help='Bypass calling reset after applying a gerrit ref.')
   parse.add_option('--specs', help='Gcilent spec.')
-  parse.add_option('--master', help='Master name.')
+  parse.add_option('--master',
+                   help='Master name. If specified and it is not in '
+                        'bot_update\'s whitelist, bot_update will be noop.')
   parse.add_option('-f', '--force', action='store_true',
                    help='Bypass check to see if we want to be run. '
                         'Should ONLY be used locally or by smart recipes.')
@@ -1725,8 +1727,13 @@ def main():
   slave = options.slave_name
   master = options.master
 
+  if not master:
+    # bot_update activation whitelist is checked only on buildbot masters.
+    # If there is no master, bot_update is always active.
+    options.force = True
+
   # Check if this script should activate or not.
-  active = check_valid_host(master, builder, slave) or options.force or False
+  active = options.force or check_valid_host(master, builder, slave)
 
   # Print a helpful message to tell developers whats going on with this step.
   print_help_text(