fix(compose): made port expose optional

Signed-off-by: Tuan-Dat Tran <tuan-dat.tran@tudattr.dev>

roles/docker_host/templates/compose.yaml.j2

@@ -10,7 +10,7 @@ services:
     networks:
       - net
 {% endif %}
-{% if service.ports is iterable %}
+{% if service.ports is defined and service.ports is iterable %}
 {% if service.ports[0].internal != 'proxy_only' %}
     ports:
 {% for port in service.ports %}