Add alert rules for CT poller.
Add alert rules for CT poller.

BUG=skia:4074

Review URL: https://codereview.chromium.org/1339353003

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