Use a name property setter instead of a set_name method

Change-Id: I4a41204e16e636e12d649592ae909d45fdb33f9f

taskflow/flow.py

@@ -46,7 +46,7 @@ class Flow(object):
         # NOTE(akarpinska): if retry doesn't have a name,
         # the name of its owner will be assigned
         if self._retry and self._retry.name is None:
-                self._retry.set_name(self.name + "_retry")
+            self._retry.name = self.name + "_retry"
 
     @property
     def name(self):

taskflow/retry.py

@@ -54,7 +54,8 @@ class Retry(atom.Atom):
     def name(self):
         return self._name
 
-    def set_name(self, name):
+    @name.setter
+    def name(self, name):
         self._name = name
 
     @abc.abstractmethod