This adds MB configs for the four verify-csa bots (gn only).

BUG=chromium:685561
NOTRY=true
NOTREECHECKS=true
TBR=danno@chromium.org, kjellander@chromium.org

Review-Url: https://codereview.chromium.org/2659583002
Cr-Commit-Position: refs/heads/master@{#42698}