Fix regression with SW deployments when region not configured

The region name eventually has to pass through an os-collect-config.conf
file, the format of which is unable to distinguish between the JSON null
(equivalent to None in Python) and the string "null".

This means that Story 2002781 caused a regression for users who didn't
have the region_name_for_services config option explicitly set in
heat.conf.

To avoid this, only specify the region when we know what it is.

Change-Id: I23493b1c477d082c478f87167de2c1859ba5ace7
Story: #2005797
Task: 33527
Task: 33528

heat/engine/resources/openstack/heat/software_deployment.py

@@ -416,9 +416,11 @@ class SoftwareDeployment(signal_responder.SignalResponder):
                 yield swc_io.InputConfig(
                     name=self.DEPLOY_PROJECT_ID, value=creds['project_id'],
                     description=_('ID of project for API authentication'))
-                yield swc_io.InputConfig(
-                    name=self.DEPLOY_REGION_NAME, value=creds['region_name'],
-                    description=_('Region name for API authentication'))
+                if creds['region_name']:
+                    yield swc_io.InputConfig(
+                        name=self.DEPLOY_REGION_NAME,
+                        value=creds['region_name'],
+                        description=_('Region name for API authentication'))
             if self._signal_transport_zaqar():
                 yield swc_io.InputConfig(
                     name=self.DEPLOY_QUEUE_ID,