Deltacloud OpenStack driver - remap 'regions' to 'providers' DTACLOUD-488

https://issues.apache.org/jira/browse/DTACLOUD-488
Deltacloud - remove unused 'resource_types' attribute from Realm model
part of DTACLOUD-488 https://issues.apache.org/jira/browse/DTACLOUD-488

API-Change: remove unused 'resource_types' attribute from Realm
DTACLOUD-477 - Remove realm<->region mapping for Openstack created Instance

https://issues.apache.org/jira/browse/DTACLOUD-477