cq.cfg: Add equivalent_to to ramp-up during LUCI migration BUG=chromium:815092 Change-Id: I5eece73be718eaaf2797c361e3d8671404f718d1 Reviewed-on: https://chromium-review.googlesource.com/957469 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>