Box Virtualbox-specific configs in 'virtualbox' module

The set of Puppet manifests and modules that ship with MediaWiki-Vagrant are
generic enough to be useful for setups other than just Vagrant on VirtualBox.
This patch concentrates all VirtualBox-specific Puppet code in a 'virtualbox'
module and ensures it is only loaded on Vagrant/Virtualbox.

Bug: 54160
Change-Id: I2a7fc2db3bbe62dbda1c4f1250674aeea135e142