Use interval Vagrant hook to determine VirtualBox version

Register a piece of middleware to run before the generic 'Provision' action to
inject the provider name & version into the Facter variable hash. Couldn't
figure out a way to do this without using a global.

Bug: 54655
Change-Id: I44a99fd3c22a85d3b62b88d7bf5d7e3ef83c8aee
Merge "Use interval Vagrant hook to determine VirtualBox version"