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=kjellander@google.com
BUG=chromium:692613
NOTRY=True

Change-Id: If10d778b9c9866593a4c6c36216ed0e1c12fa1d5
Reviewed-on: https://chromium-review.googlesource.com/443546Reviewed-by: Henrik Kjellander <kjellander@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

infra/config/cq.cfg

@@ -15,6 +15,11 @@ rietveld {
 verifiers {
   reviewer_lgtm {
     committer_list: "project-libyuv-committers"
+    dry_run_access_list: "project-libyuv-tryjob-access"
+  }
+  gerrit_cq_ability {
+    committer_list: "project-libyuv-committers"
+    dry_run_access_list: "project-libyuv-tryjob-access"
   }
 
   try_job {