Also use low experiment percentage on CQ, since the builder's output is unused.

NOTRY=true
TBR=sergiyb@chromium.org

Bug: chromium:830557
Change-Id: Id024ab16e2944ec5e94b0209672ed6b77ae322a8
Reviewed-on: https://chromium-review.googlesource.com/c/1296466Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56947}