Fix UnboundLocalError local variable 'success' referenced before assignment
Fix UnboundLocalError local variable 'success' referenced before assignment

https://console.cloud.google.com/errors/CPzek-PWo9r-sgE?time=PT1H&project=chromium-swarm

Fixed: 1234636
Change-Id: Iad9aa04062fd3a304f08c6d208cb78273bdf03f4
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/3062144
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py