Send browser and email notifications of pipeline failures earlier

Currently browser and email notifications for pipeline failures get sent out after the entire pipeline has finished with a failure state, but this can happen long after the eventual failure of a pipeline was known. e.g. when the static-analysis job fails during the test stage of our CI config, it may still be quite some time before all of the other jobs in that stage are complete. I could have been notified and started working on a fix much sooner had I been notified.

Perhaps we should change the behavior of these notifications to come as soon as the first job fails.

/cc @DouweM