[swarming] Reduce log severity for small bots.cfg expiration
[swarming] Reduce log severity for small bots.cfg expiration

This config 'expires' all the time but a sub second expiration is fine
and expected. Only log an warning when the delay is significant, like
over 5 seconds. Otherwise filtering logs per warning+ entries are
overwhelmed by this one.

R=747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org

Change-Id: I65f047f73fba5fe459d9c0608a4e758153a8dc50
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1506232
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

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