Some fixes (#41)

* Fix the sample inventory

The `openstack_nameservers` variable needs to be a list of strings, we
need to set the Openshift labels in OSv3.yml and we show an example of
using the username/password/poll for RHEL subscriptions.

* Update the READMEs

This fixes some of the paths, explains that we need to pass
`openstack_ssh_public_key` to the end-to-end playbook and includes the
full Docker command since there is no `run.sh` script.  Oh and Heat is
not an acronym :).

* Fixes to the readme and inventory

* Use docker-compose