The python network script isn' based on exception but return values

* postservice/31-one-netmng (OneClient.create_network): make sure to
  return True since the returned value is checkd in
  “OneNetwork.create()”.

Ref: #24531

postservice/31-one-netmng

@@ -130,9 +130,9 @@ class OneClient():
             if not res:
                 print("Error attaching {0} vnet to {1} cluster".format(vnet_name, cluster))
                 return False
-
-            os.remove(templatefile)
-
+            else:
+                os.remove(templatefile)
+                return True
         else:
             logger.error(u"Creation of virtual network with template {0} failed".format(templatefile))
             return False