Check group metadata for autoscaling completion

In f3eec740a8820ecf96561c9491672787c449469d we changed to set
group resource metadata rather than policy. Therefore we should
check that instead.

Change-Id: I05b309cd7dccac62183976290217cfe78edd4d48
diff --git a/heat_tempest_plugin/common/test.py b/heat_tempest_plugin/common/test.py
index 4fdfb8e..de7f25a 100644
--- a/heat_tempest_plugin/common/test.py
+++ b/heat_tempest_plugin/common/test.py
@@ -712,13 +712,13 @@
             time.sleep(build_interval)
 
     def check_autoscale_complete(self, stack_id, expected_num, parent_stack,
-                                 policy):
+                                 group_name):
         res_list = self.client.resources.list(stack_id)
         all_res_complete = all(res.resource_status in ('UPDATE_COMPLETE',
                                                        'CREATE_COMPLETE')
                                for res in res_list)
         all_res = len(res_list) == expected_num
         if all_res and all_res_complete:
-            metadata = self.client.resources.metadata(parent_stack, policy)
+            metadata = self.client.resources.metadata(parent_stack, group_name)
             return not metadata.get('scaling_in_progress')
         return False