Try to make the play faster and more repeatable
Install skydns and skydock

* Skydns servers are configured in a cluster. This requires a new
`dns_leader` Ansible variable.

* Skydock is run on each server and talks to the master skydns (it
should talk to the local one, but a bug in the skydns code prevents it,
see comments)
* Some updates to the README
A couple of scripts to make it easier to build / test

* fresh-start.sh : shuts down, removes and ups all Vagrant hosts
* build.sh:  runs the ansible play. Any arguments will be passed to
ansible