Fix fake_kitchen.sh on windows.
Fix fake_kitchen.sh on windows.

`logdog_butler` apparently likes the non-absolute path (and the path
prefix here was wrong anyway :)).

R=a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org

Bug: 910369
Change-Id: I7df52cc51029b05a0b5c0815020d1aae4e8460f9
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/recipes-py/+/1642339
Auto-Submit: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>

luci/recipes-py,luci/recipes-py