Prior to this commit, the hyper-v and virtualbox system crash check
existed within the initialize function of the virtualbox provider. That
caused an issue when running with other providers, because the
virtualbox provider still gets initialized even if not used. This commit
changes that by placing the check inside of one of the virtualbox
provider actions that checks if virtualbox is installed and ready to
use. This action is action is used by the main vbox provider actions,
and should not be called when other providers are being used with
Vagrant.
Brian Cain
Mitchell Hashimoto