Do a final clean of the pacman cache, then write zeros to disk and
unlink the file. Packer will compact the disk as part of the build,
resulting in a smaller final image.
Instead of having mostly duplicate scripts for the entire installation
process, we can split them up into the base installation steps and then
run shell provisioners for anything specific to each of the types after
the machine has rebooted.
This structure will mean less chance of error when making changes to
machines, and will also allow for expansion of the scripts to be run at
the end, such as adding a minimization script to remove history and
clear out space on the drive before compression.
