Limit CI results to the owner when things are good.
Limit CI results to owner + reviewers when things are not so good.

Should reduce email spam.

Change-Id: I1b71f17f306bf04ecb9fb87ffd95aea42a8e84b4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39308Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>