Prefer OpenStack Regions

This PR removes all references to "zone" in the OpenStack APIs in favor of the common "region" nomenclature as described in [JCLOUDS-647](https://issues.apache.org/jira/browse/JCLOUDS-647).

This PR will need a squash after its reviewed!
I am in the process of refactoring the OpenStack Live tests to use a new base class. It will be addressed in that PR, since there is more work to do moving to regions.