[autoroll] Don't send duplicate "Last N rolls failed" notifications
[autoroll] Don't send duplicate "Last N rolls failed" notifications

Change-Id: Id5aa7cb10c2ae3521542a5127119c29bad4b2218
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/211060
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot