* don't retry successful (last build) or still running builders.
* don't retry CQ experimental builders.

R=ehmaldonado

Bug: 1012631
Change-Id: I2a155b274c822f8ead032098a08702f26362bee3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1851735Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@google.com>