Avoid not_done naming conflict

In order to make understanding the
usage of the 'not_done' variable easier
allow the schedule to take in the list
it will be appending to instead of relying
on a function local variable (which is
overwritten in the contained while loop)

Change-Id: I60c0c970d8fb444983e0d8b567ebe82c47e13d96

taskflow/engines/action_engine/graph_action.py

@@ -59,20 +59,18 @@ class FutureGraphAction(object):
         return st.SUSPENDED if was_suspended else st.REVERTED
 
     def _run(self, running, schedule_node, complete_node, get_next_nodes):
-        not_done = []
 
-        def schedule(nodes):
+        def schedule(nodes, not_done):
             for node in nodes:
                 future = schedule_node(node)
                 if future is not None:
                     not_done.append(future)
                 else:
-                    schedule(get_next_nodes(node))
-
-        schedule(get_next_nodes())
+                    schedule(get_next_nodes(node), not_done)
 
         failures = []
-
+        not_done = []
+        schedule(get_next_nodes(), not_done)
         was_suspended = False
         while not_done:
             # NOTE(imelnikov): if timeout occurs before any of futures
@@ -93,7 +91,7 @@ class FutureGraphAction(object):
 
             if next_nodes:
                 if running() and not failures:
-                    schedule(next_nodes)
+                    schedule(next_nodes, not_done)
                 else:
                     # NOTE(imelnikov): engine stopped while there were
                     # still some tasks to do, so we either failed