fix error message: '[/etc/systemd/system/docker.service.d/docker-options.conf:3] Failed to parse mount flag , ignoring.'

roles/docker/templates/docker-options.conf.j2

@@ -1,6 +1,5 @@
 [Service]
-Environment="DOCKER_OPTS={{ docker_options | default('') }} \
---iptables=false"
+Environment="DOCKER_OPTS={{ docker_options | default('') }} --iptables=false"
 {% if docker_mount_flags is defined and docker_mount_flags != "" %}
 MountFlags={{ docker_mount_flags }}
 {% endif %}