Use Checks API for discovering changes to build

Enable the filtering by pending checks, allowing to
discover the changes that need validation only.

In order to keep the build logs of older job runs, disable
the drop of old branches jobs and keep them around for
up to 3 months or 500 runs overall.

Change-Id: Ic92253b7c225dd8fbdeffb16d433928d667ccdea
diff --git a/jenkins/gerrit-verifier.yaml b/jenkins/gerrit-verifier.yaml
index 25b7fc7..ebdbc3f 100644
--- a/jenkins/gerrit-verifier.yaml
+++ b/jenkins/gerrit-verifier.yaml
@@ -140,12 +140,18 @@
     description: Multi-branch pipeline to validate Gerrit
     project-type: multibranch
     node: master
+    days-to-keep: 90
+    number-to-keep: 500
+    prune-dead-branches: false
     scm:
       - gerrit:
           url: https://gerrit-review.googlesource.com/a/gerrit
           credentials-id: gerrit-review.googlesource.com
           refspecs:
             - '+refs/heads/*:refs/remotes/@{remote}/*'
+          filter-checks:
+            query-operator: 'SCHEME'
+            query-string: 'gerritforge'
           property-strategies:
             all-branches:
               - suppress-scm-triggering: false