[tsmon] Recognize k8s and GCLB health checkers as robots.
[tsmon] Recognize k8s and GCLB health checkers as robots.

R=tandrii@chromium.org

Change-Id: I45014681bc64c1d5aa258885987fb53bca6cefb7
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1984611
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go