L2SS-645: Added mock for additional asyncua function that we now use

tangostationcontrol/tangostationcontrol/test/clients/test_opcua_client.py

@@ -86,6 +86,7 @@ class TestOPCua(base.AsyncTestCase):
         m_opc_client_members.send_hello = asynctest.asynctest.CoroutineMock()
         m_objects_node = asynctest.Mock()
         m_objects_node.get_child = asynctest.asynctest.CoroutineMock()
+        m_objects_node.get_children_descriptions = asynctest.asynctest.CoroutineMock()
         m_opc_client_members.get_objects_node = asynctest.Mock(return_value=m_objects_node)
         m_opc_client.return_value = m_opc_client_members