Author: Jonas Pfannschmidt
Email: jonas.pfannschmidt at gmail.com
Copying a vagrant image to another machine can be tricky and you usually shouldn't do that at all. The whole point of vagrant is to reproducible create and provision VMs from only the Vagrantfile.
If for whatever reason you need to do it anyway, here are the steps (Main source: http://stackoverflow.com/questions/19094024/is-there-any-way-to-clone-a-vagrant-box-that-is-already-installed)
Note: The VM will be restarted during this process. You'll loose anything ephemeral!