use multiline string for dockerengine_service_override_unit

defaults/main.yml

@@ -18,7 +18,16 @@ dockerengine_ansible_deps:
   - docker
 
 dockerengine_service: docker
-dockerengine_service_override_unit: []
+
+# @var dockerengine_service_override_unit:description: >
+# Multiline string of options to add to the `systemd` service override unit section.
+# @end
+# @var dockerengine_service_override_unit: $ "_unset_"
+# @var dockerengine_service_override_unit:example: >
+# dockerengine_service_override_unit: |
+#   After=time-sync.target
+#   Requires=time-sync.target
+# @end
 
 dockerengine_docker_group_enabled: False
 

templates/etc/systemd/system/docker.service.d/override.conf.j2

@@ -1,10 +1,9 @@
 #jinja2: lstrip_blocks: True
 {{ ansible_managed | comment }}
-{% if dockerengine_service_override_unit | default([]) | length > 0 %}
+{% if dockerengine_service_override_unit is defined %}
 [Unit]
-{% for item in dockerengine_service_override_unit %}
+{{ dockerengine_service_override_unit }}
-{{ item }}
+{% endif %}
-{% endfor %}
 [Service]
 EnvironmentFile=-/etc/sysconfig/docker
 ExecStart=