Fix imports for test_simultaneous_update

Change-Id: Ide957859f88bcfc9e15057c57d520245023e265d
diff --git a/heat_tempest_plugin/common/test.py b/heat_tempest_plugin/common/test.py
index 7db874b..d719ad0 100644
--- a/heat_tempest_plugin/common/test.py
+++ b/heat_tempest_plugin/common/test.py
@@ -73,7 +73,8 @@
 
     The decorated test will be skipped when convergence is disabled.
     '''
-    convergence_enabled = config.CONF.heat_plugin.convergence_engine_enabled
+    plugin = config.CONF.orchestration_plugin
+    convergence_enabled = plugin.convergence_engine_enabled
     skipper = testtools.skipUnless(convergence_enabled,
                                    "Convergence-only tests are disabled")
     return skipper(test_method)