Make PythonParser's on_disconnect consistent with

Hiredisparser and Connection — do not close socket on disconnect.
Resolves #1085

Author: popravich

redis/connection.py

@@ -276,9 +276,7 @@ def on_connect(self, connection):
 
     def on_disconnect(self):
         "Called when the socket disconnects"
-        if self._sock is not None:
-            self._sock.close()
-            self._sock = None
+        self._sock = None
         if self._buffer is not None:
             self._buffer.close()
             self._buffer = None