Network cache is not flushed on deploying host when containers are destroyed

[Shu Shen]

lxc-container-destroy.yml performs flush-net-cache by delegate to lxc host.

In a multiple host deployment, the deploying host (which runs the playbooks) may not be the host for the containers being destroyed. Therefore, flush-net-cacahe is not performed on the deploying host.

This would cause connectivity problem between the deploying host and the containers before the staled net cache timed out ultimately.