Make errors in PerformBisect non-fatal in auto_bisect handler.
Make errors in PerformBisect non-fatal in auto_bisect handler.

In general, /auto_bisect should keep on trying to restart bisect jobs no matter what kind of error happens when trying to restart bisect jobs.

BUG=catapult:#1661

Review URL: https://codereview.chromium.org/1412313012

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