Make spun up instances easier to use as custom Vagrant base box

The Vagrant keypair is not the default added to new machines created
by stratus with the private key located at keys/vagrant.

Add your public key to keys/authorized_keys if you'd like to restore
the old functionality or use a different keypair.
Removed flakey DNS zone update support
Update readme to correctly reflect recent functionality changes
Merge branch 'master' of github.com:bradleybeddoes/stratus