[scheduler] Add adhoc script to detect jobs with stuck ActiveInvocations list.
[scheduler] Add adhoc script to detect jobs with stuck ActiveInvocations list.

R=a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org
BUG=852142

Change-Id: Idae7f05c5045a72ff85db8587f8bd74c0b80fb06
Reviewed-on: https://chromium-review.googlesource.com/1098463
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

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