We don't need vm-tools, and the latest version of Virtualbox actually
causes a kernel panic with our old kernel. This moves back to an older
base, uses SHA256 to download it, and disables vm-tools.
Fixes#318
There were quite a few bugs in the chef recipes when building using other platforms.
These were mostly due to assuming the vagrant user would exist.
Things are now more generic and should be more reliable overall.
This makes some other changes:
* Moves packer related files to packer directory.
* Updates build scripts for new packer directory.
* Renames boxes to metasploitabl3-<OS>