It looks like we often list the branch twice WITH DIFFERENT VALUES in both cbuildbot_launch invocation, and when invoking cbuildbot.

Since we list the real value second, this works, but is confusing and ugly.

Swarming example:

Cmd:
  cros tryjob --swarming -g 858174 --branch release-R65-10323.B lumpy-compile-only-pre-cq

Build:
  http://cros-goldeneye/chromeos/healthmonitoring/buildDetails?buildbucketId=8955209776461890624

cbuildbot_launch:
  /b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch --buildroot /b/swarming/w/ir/cache/cbuild --branch master --buildbucket-id 8955209776461890624 --git-cache-dir /b/swarming/w/ir/cache/git --goma_dir /b/swarming/w/ir/cache/goma_client --goma_client_json /creds/service_accounts/service-account-goma-client.json --remote-trybot -b release-R65-10323.B -g 858174 lumpy-compile-only-pre-cq