[swarming] log queue numbers found during _rebuild_bot_cache_async
[swarming] log queue numbers found during _rebuild_bot_cache_async

Context: https://crbug.com/1064848#c28

Bug: 1064848
Change-Id: I39d122047d30219113bc03f896ebbdc5b6a94ff2
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2162419
Commit-Queue: Ye Kuang <1cd89f22f3967fc3dcb883b53940be4b98ec483f@google.com>
Reviewed-by: Ye Kuang <1cd89f22f3967fc3dcb883b53940be4b98ec483f@google.com>
Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

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