Move ldap image to separate file as it's not always required

Include classes with jenkins images into stack definition.
Change-Id: I34c3033e88a030cacc476c2fc8337c9b78ef5558
Related-bug: #PROD-25515 (PROD:25515)
diff --git a/docker/swarm/stack/jenkins/slave_base.yml b/docker/swarm/stack/jenkins/slave_base.yml
index 630dd14..648a572 100644
--- a/docker/swarm/stack/jenkins/slave_base.yml
+++ b/docker/swarm/stack/jenkins/slave_base.yml
@@ -1,3 +1,5 @@
+classes:
+- system.docker.client.images.jenkins_slave
 parameters:
   _param:
     jenkins_master_host: ${_param:control_vip_address}