Use the misc.ensure_dict helper in conductor engine options saving

Change-Id: I7d796f4ca4b59a22fdae417f1483b3778d3070d0

taskflow/conductors/base.py

@@ -46,10 +46,7 @@ class Conductor(object):
         self._name = name
         self._jobboard = jobboard
         self._engine = engine
-        if not engine_options:
-            self._engine_options = {}
-        else:
-            self._engine_options = engine_options.copy()
+        self._engine_options = misc.ensure_dict(engine_options)
         self._persistence = persistence
         self._lock = threading.RLock()
         self._notifier = notifier.Notifier()