openshift_docker role was largely useless now, but also almost did what
we needed. (deps ordering still needs to be changed)

Remove defaulting of openshift_version.

Mostly necessary for debugging / testing upgrade paths

- Add support to bin/cluster for specifying etcd hosts
  - defaults to 0, if no etcd hosts are selected, then configures embedded
    etcd
- Updates for the byo inventory file for etcd and master as node by default
- Consolidation of cluster logic more centrally into common playbook
- Added etcd config support to playbooks
- Restructured byo playbooks to leverage the common openshift-cluster playbook
- Added support to common master playbook to generate and apply external etcd
  client certs from the etcd ca
- start of refactor for better handling of master certs in a multi-master
  environment.
  - added the openshift_master_ca and openshift_master_certificates roles to
    manage master certs instead of generating them in the openshift_master
    role
- added etcd host groups to the cluster update playbooks
- aded better handling of host groups when they are either not present or are
  empty.
- Update AWS readme