Don't fail veth-cleanup template when no container_networks
Don't fail veth-cleanup template when no container_networks

veth-cleanup template is broken if container_networks is not defined,
ie. if I have a container with eth0/LXC base nat network only.

Change-Id: I19663e0a32466c54b1b6ba9fadf243aed8055b7e

openstack/openstack-ansible-lxc_container_create,openstack/openstack-ansible-lxc_container_create