Trybot ingestion - handle deleted Patchsets
Trybot ingestion - handle deleted Patchsets

This fixes the case when a patchset that has trybot runs associated with it, is deleted from the CL.
If it cannot retrieve the patchset it checks whether the parent CL exists, if it does it issues a warning and ignores the results of the deleted patchset.

BUG=skia:5218

Review URL: https://codereview.chromium.org/1915143003

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