Use type separate as work-around for VirtualBox 5.1.6
Use type separate as work-around for VirtualBox 5.1.6

With VirtualBox 5.1.6, console type "headless" often gives no access to
the VM console which on Windows is the main method for interacting with
the cluster. Use "separate" for Windows batch files, which works at
least on 5.0.26 and 5.1.6.

Change-Id: Ib907ef2ac947547b7cce762a8426c92bb62f1abb

openstack/training-labs,openstack/training-labs,openstack/training-labs