EnginePort: use %s format instead of %d in __repr__() (#500)

Use more robust formatting in case the streams are not initialized yet.

Fixes #499.

Author: thiell

lib/ClusterShell/Worker/EngineClient.py

@@ -499,7 +499,7 @@ def __repr__(self):
             fd_out = self.streams['out'].fd
         except KeyError:
             fd_out = None
-        return "<%s at 0x%s (streams=(%d, %d))>" % (self.__class__.__name__, \
+        return "<%s at 0x%s (streams=(%s, %s))>" % (self.__class__.__name__,
                                                     id(self), fd_in, fd_out)
 
     def _start(self):