Improve the config-update using smart-reconfigure

This change makes the config-update significantly faster by
skipping project which didn't change.

Change-Id: Ibcc73932f7bd705f1b49d4c8e23937d8c356d380

Author: TristanCacqueray

controllers/static/git-server/update-system-config.sh

@@ -166,7 +166,7 @@ cat << EOF > playbooks/config/update.yaml
     - name: "Update zuul tenant config"
       command: /usr/local/bin/generate-zuul-tenant-yaml.sh "{{ config_ref }}"
     - name: "Reconfigure the scheduler"
-      command: zuul-scheduler full-reconfigure
+      command: zuul-scheduler smart-reconfigure
 
 - hosts: nodepool-launcher
   vars: