Fix for not released thread in get_session_client

The thread that is created in the 'network_adapter' is never released,
we should use task_manager.stop() to release unnecessary resources.
If not released each connection to service will create a threadpool
that is not detected by the garbage collector.

Change-Id: Iefb2fc55caf38eed5f79aec3622c21e80be5936b
Story: 28885

openstack/config/cloud_region.py

@@ -492,6 +492,7 @@ class CloudRegion(object):
                     region_name=self.region_name,
                 )
                 network_endpoint = network_adapter.get_endpoint()
+                network_adapter.task_manager.stop()
                 if not network_endpoint.rstrip().rsplit('/')[-1] == 'v2.0':
                     if not network_endpoint.endswith('/'):
                         network_endpoint += '/'