[BENTO-41] Check to see if you're on VirtualBox

Because vagrant is now multi-provider, you might not want these
installed.
Fix PR#33 - CentOS 5.8 is in the vault now. Thanks @someara.
Merge pull request #52 from juliandunn/centos-5.8-vault

Fix PR#33 - CentOS 5.8 is in the vault now.
[BENTO-19] Use the VirtualBox ISO that veewee attaches to the machine, rather than wgetting it. Also, retrieve the vagrant key over https.
Merge branch 'BENTO-19' of github.com:juliandunn/bento into BENTO-19

Conflicts:
	definitions/.common/vagrant.sh