Packer provisioning for warden compatible boxes

This includes a packer template and provisioning scripts to create warden-compatible boxes for vmware and virtual box.  The box consists of:

* Ubuntu 12.04.4 and the latest kernel
* cgroup memory limits and accounting as required for 12.04.4
* kernel hold to prevent automatic updates (avoids VMware tools issues)
* warden-test-infrastructure provisioning via the existing project cookbooks

This is a starting point and needs some cleanup but it would be great to get some input on what's here already in support of https://www.pivotaltracker.com/s/projects/966314.  I've used this box for testing warden and the dea without issue.