[pinpoint] Use False/True for pass/fail when doing MWU for functional bisects.
[pinpoint] Use False/True for pass/fail when doing MWU for functional bisects.

Testing showed that yes, there is enough variability between exception strings
that they will cause Pinpoint to bisect in the wrong place. Better to stick with
just pass/fail.

https://pinpoint-dot-chromeperf.appspot.com/job/14fdf793b80000
Review-Url: https://chromiumcodereview.appspot.com/3010393003

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult