Add sub_nodes and node_private files in /etc/nodepool
Add sub_nodes and node_private files in /etc/nodepool

TripleO-CI uses these for things.

Change-Id: Id2fd8d0a0aeedfaedf84004dbab61e9988163fa7

openstack-infra/openstack-zuul-jobs,openstack-infra/openstack-zuul-jobs