chromite: Send notification emails on lakitu build failures

This should work according to
https://chromium.googlesource.com/chromiumos/chromite/+/master/lib/config_lib.py#442.

Starting with incremental and release builders, as the former catch problems
early enough and the latter have additional stages whose failures won't be
caught in incremental builders. Paladin and pre-cq failures are not alerted as
they are expected to fail from time to time.

BUG=b:27138853
TEST=Trybots to verify the change doesn't break existing functionalities.
    However it would require a buildbot failure to verify it has its expected
    functionality since tryjobs won't trigger email alerts.

Change-Id: Id0d88279a6cfa6f1e9e5e8399e99b3941b3a86ef
Reviewed-on: https://chromium-review.googlesource.com/414198
Commit-Ready: Daniel Wang <wonderfly@google.com>
Tested-by: Daniel Wang <wonderfly@google.com>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Reviewed-by: Ningning Xia <nxia@chromium.org>
Reviewed-by: Amey Deshpande <ameyd@google.com>
2 files changed