Handle null region
Handle null region

Not all clouds define/require region_name to be set

dtroyer/os-client-config,redhat-openstack/os-client-config,switch-ch/os-client-config,dtroyer/python-openstacksdk,openstack/os-client-config,openstack/python-openstacksdk,openstack/python-openstacksdk,stackforge/python-openstacksdk,dtroyer/python-openstacksdk,stackforge/python-openstacksdk,emonty/os-client-config