Fixes devstack ldap plugin

When the ldap service is enable on local.conf devstack ldap
plugin starts slapd service using its default config on Ubuntu
and installs ldap-utils package.
Enables domain specific drivers on Keystone and creates LDAP
domain 'Users' with a demo user.

Change-Id: I8d7aa260b01f675e4ed201ef93bfd66474f4b228
diff --git a/lib/horizon b/lib/horizon
index 9c7ec00..becc5a0 100644
--- a/lib/horizon
+++ b/lib/horizon
@@ -106,6 +106,10 @@
         _horizon_config_set $local_settings "" OPENSTACK_SSL_CACERT \"${SSL_BUNDLE_FILE}\"
     fi
 
+    if is_service_enabled ldap; then
+        _horizon_config_set $local_settings "" OPENSTACK_KEYSTONE_MULTIDOMAIN_SUPPORT "True"
+    fi
+
     # Create an empty directory that apache uses as docroot
     sudo mkdir -p $HORIZON_DIR/.blackhole