Prevent branch-util from being run on the remote trybots.

We don't want everyone to create branches, and we want to rely on
gerrit's ACL's to control branch creation.  So prevent --remote jobs for
branch-util.  This is not meant has a strong means of prevention, only
one layer of deterrent, useful for preventing users from accidentally
launching remote tryjobs.

BUG=chromium:260969
TEST=Locally

Change-Id: I880cde1dfa26b6fd9c574cf277b61e6598d1f880
Reviewed-on: https://gerrit.chromium.org/gerrit/65260
Reviewed-by: Matt Tennant <mtennant@chromium.org>
Commit-Queue: Ryan Cui <rcui@chromium.org>
Tested-by: Ryan Cui <rcui@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index a9c75a9..4a54d1e 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -1184,6 +1184,9 @@
   options.build_targets = args[:]
 
   if constants.BRANCH_UTIL_CONFIG in options.build_targets:
+    if options.remote:
+      cros_build_lib.Die(
+          'Running branch-util as a remote tryjob is not yet supported.')
     if len(options.build_targets) > 1:
       cros_build_lib.Die(
           'Cannot run branch-util with any other configs.')