Packer provisioning for warden compatible boxes

* Ubuntu 12.04.4 with latest kernel
* Enables cgroup memory limits and accounting for 12.04.4
* Locks the kernel to prevent automatic updates
* Executes warden-test-infrastructure recipes
Merge remote-tracking branch 'origin/pr/7'

Signed-off-by: Kai Zhang <kaizhang@cn.ibm.com>
Switch to packer for creating warden-compatible.box in CI
- virtualbox only in CI for the moment
- vmware is possible
- added basic instructions to README
- [#69539058]

Signed-off-by: Kai Zhang <kaizhang@cn.ibm.com>