nodedev: remove useless exception instance

Commit f341352cda
removed redundant error string,
so the instance 'e' in exception is useless.
Just delete it.

Signed-off-by: Chen Hanxiao <chenhanxiao@gmail.com>

virtinst/nodedev.py

@@ -84,7 +84,7 @@ class NodeDevice(XMLBuilder):
 
         try:
             return _AddressStringToNodedev(conn, idstring)
-        except Exception, e:
+        except Exception:
             logging.debug("Error looking up nodedev from idstring=%s",
                 idstring, exc_info=True)
             raise