CQ config: add gerrit CQAbility verifier.

Goal is to ensure that unreviewed and untrusted code isn't sent through
CQ to try bots, by accident or through malicious intent.

R=agable@chromium.org
BUG=692613

Change-Id: I3f202685dff1ba0d609fadfd5725f98be833d325
Reviewed-on: https://chromium-review.googlesource.com/443351
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

infra/config/cq.cfg

@@ -16,6 +16,10 @@ verifiers {
     committer_list: "project-infra-committers"
     dry_run_access_list: "project-infra-tryjob-access"
   }
+  gerrit_cq_ability {
+    committer_list: "project-infra-committers"
+    dry_run_access_list: "project-infra-tryjob-access"
+  }
 
   try_job {
     buckets {