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
This makes AWS the default provider for cluster.sh.

@jwhonce is that desired?  I thought gce was going to remain the default, at least for now.