Ensure openstack_hosts sets nodepool variables
Ensure openstack_hosts sets nodepool variables

This patch ensures that openstack_hosts gate jobs use the nodepool
variables set within openstack-ansible-tests.

Closes-Bug: 1748253
Change-Id: I343eea459aa8992e80291486decb03db4e224202

openstack/openstack-ansible-openstack_hosts,openstack/openstack-ansible-openstack_hosts