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)
(cherry picked from commit 555d42ff8bdce31cdccdbcb8bbf62871df75c5b6)
diff --git a/docker/swarm/stack/ldap.yml b/docker/swarm/stack/ldap.yml
index 14e8b37..fbb74bc 100644
--- a/docker/swarm/stack/ldap.yml
+++ b/docker/swarm/stack/ldap.yml
@@ -1,3 +1,5 @@
+classes:
+- system.docker.client.images.ldap
 parameters:
   docker:
     client: