labs: export only nodes that we built
labs: export only nodes that we built

Don't export all cluster nodes but only those that the script actually
built.

Change-Id: I9dcd778606e4f434a688fe536fc1b7421b8972aa

Nabs007/training-guides,harrisonfeng/training-guides,Nabs007/training-guides,openstack/training-guides,harrisonfeng/training-guides,Nabs007/training-guides,harrisonfeng/training-guides,openstack/training-guides