Adding AWS support to openshift-ansible module

- Update documentation to say that ssh configuration need to point to the private key file
- Removing the -p argument when calling time .... because it is misintrepreted by ruby
- Turning the cluster.sh to agnostic in its help/error message by replacing explicit reference to GCE by a a variable
- Fixing a bug within the playbooks that incorrectly references the minions and master fact group. Needs a better fix with a call to AWSHelper.generate_env_host_type_tag_name()
- Adding playbooks for AWS, which are almost of copy/paste for those of GCE: Needs a refactor to reduce code duplication
I'm fine with allowing an environment variable to override it. Make sure to prefix the environment variable name, so that it's unique. We usually use OO_ as a prefix.