Ability to build VirtualBox images with i386 and amd64 architectures

Created by: vignanl

The changes in this branch introduce the ability to build VirtualBox images for both i386 and amd64 architectures. The target virtualbox still builds the i386 architecture image. To build amd64 image the target is virtualbox-amd64.

Both images have been tested by building and booting them in VirtualBox.

Created by: SunilMohanAdapa

Vignan worked with me on this and I have reviewed his changes. I find them to be positive change and correct.