This is a reland of 331a276b
Original change's description:
> bot_update: make --output_json required in script invocation.
> 
> It's already set by recipe, so this should have 0 difference in prod.
> 
> R=iannucci@chromium.org
> 
> Bug:
> Change-Id: I1e1129b9748d6647e45eb26892c8e892019fe088
> Reviewed-on: https://chromium-review.googlesource.com/769164
> Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
> Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

Change-Id: I165da9650df6b5e8d382aafc30914eff9a524c56
Reviewed-on: https://chromium-review.googlesource.com/777820Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>