harmonize execute_graph output

ewoksppf/tests/test_ppf_workflow9.py

 from ewoksppf import execute_graph
-from ewokscore.tests.utils.results import assert_execute_graph_all_tasks
+from ewokscore.tests.utils.results import assert_execute_graph_default_result
 
 
 def workflow9():
@@ -58,5 +58,5 @@ def workflow9():
 def test_workflow9(ppf_log_config, tmpdir):
     varinfo = {"root_uri": str(tmpdir)}
     graph, expected = workflow9()
-    execute_graph(graph, varinfo=varinfo)
-    assert_execute_graph_all_tasks(graph, expected, varinfo=varinfo)
+    result = execute_graph(graph, varinfo=varinfo)
+    assert_execute_graph_default_result(graph, result, expected, varinfo=varinfo)