Use the 'gerrit' choosing-strategy so code is properly checked

Change-Id: I73634002cb6732d7bc4662ef97d784a4dc4563b9
diff --git a/jjb/charts.yaml b/jjb/charts.yaml
index b8c74a9..b250975 100644
--- a/jjb/charts.yaml
+++ b/jjb/charts.yaml
@@ -41,7 +41,7 @@
           refspec: ''
           branch: '$GERRIT_BRANCH'
           submodule-recursive: 'false'
-          choosing-strategy: default
+          choosing-strategy: 'gerrit'
           jenkins-ssh-credential: '{jenkins-ssh-credential}'
 
     node: '{build-node}'