[swarming] Add log for poll request deduplication
[swarming] Add log for poll request deduplication

Bug: 1214700
Change-Id: If94f640bc813895e8e2ad1f1eeb2eb47cb140cb3
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/3160043
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