Fix failing perf backup cronjob.
Fix failing perf backup cronjob.

Running this script as a CronJob is reported as an error, but looking at the
logs it always succeeds, so try forcing a happy exit code.

Change-Id: I87b7a8ab20dcd11f64b6b0d4636f3ed896f45884
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/573939
Auto-Submit: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@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