Add Vagrantfile for testing warden using warden-test-infrastructure on AWS

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
Move Vagrantfile back to root

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
Use environment for private key location

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>