* make guest tools last so pre-reqs are in place
Packer 1.3.x and possibly more does not inject enviornment
variables as expected into `windows-shell` provisioners, moving
script that requires these into a `shell` provisioner.
* do not trust default uploaded windows.iso
Packer in some cases will upload windows.iso from the host
building the VM, since server 2008 needs a specific older
version of tools this can cause problems.
Example issue:
VMware Fusion 11 on macOS Mojave will supply 10.3.x in windows.iso
and will hit https://kb.vmware.com/s/article/55798 due the patch level
expectaions that are intentionally not met for Windows 2008r2.
This makes some other changes:
* Moves packer related files to packer directory.
* Updates build scripts for new packer directory.
* Renames boxes to metasploitabl3-<OS>
