branch-util: Fix branch-util-tryjob for testing.

branch-util has lots of special handling, which was broken for
branch-util-tryjob. Add the new config to the special case handling.

BUG=chromium:784985
TEST=cros tryjob --cbuildbot branch-util-tryjob --branch-name test_branch --version 10127.0.0

Change-Id: Id60bfbf54148ede3d7af2da732c630df78c7c088
Reviewed-on: https://chromium-review.googlesource.com/769658
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index f63d6d1..c67cfbb 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -625,7 +625,8 @@
   # We force --debug to be set for builds that are not 'official'.
   options.debug = options.debug or not options.buildbot
 
-  if constants.BRANCH_UTIL_CONFIG == options.build_config_name:
+  if options.build_config_name in (constants.BRANCH_UTIL_CONFIG,
+                                   'branch-util-tryjob'):
     if not options.branch_name:
       cros_build_lib.Die(
           'Must specify --branch-name with the %s config.',