simplify vbox_create.sh

* Utilize Packer for bcpc-bootstrap node
* Simplify creation of worker VMs
* Decouple bootstrap_chef.sh and enroll_cobber.sh from Vagrant
* remove Vagrant as a means of setting up local development install.
  Packer-based builds provide the image once built
remove scripts that were specific to Vagrant
update bootstrap.md with latest documentation

* Remove usage/mentioning of Vagrant
* Mention Packer used for the bcpc-bootstrap image
* Removed all the alternative paths to simplify installation