Virtualbox Vagrant boxes may be built

I've done this in a couple different places before, and each time I
re-invent the same basic script, heavily influenced from OpsCode's Bento

This provides a way to build a builder host that can be used with
vagrant. If the project would need to be deployed on to AWS, you may
consider using an AWS builder.
Annotates build_host packer file
Renames directory to match packer file
Documents usage of the builder_host
Enables docker at vm startup

I apparently left this out. Oops!
Remove comments because packer won't run with them
Merge pull request #1 from zspencer/use-packer-to-build-vagrant-machine

Packer builds VM for builder host