Changes needed for AWS AMI (Amazon Web Services Amazon Machine Image):

  If a virtual box is used then the config.ssh.username is "vagrant".
  However if other boxes are used then the config.ssh.username may not be "vagrant", in particular, the Ubuntu AMI uses "ubuntu".

  Instead of hard coding in the owner and group in the puppet files,  the Vagrantfile checks to see what the box is, and then passes to puppet by factering the value for git_owner and git_group.

  ENV['BUILD'] is used as a switch between virtual boxes and AMI boxes.