[swarming] add debug logs to _yield_potential_tasks()
[swarming] add debug logs to _yield_potential_tasks()

Bug: 1064848
Change-Id: I4f97089a727e2a2fbd870ad506fa6b4b169934ff
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/3252624
Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

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