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
(cherry picked from commit 7310b0bc9e)
61d1f7e8c4