Close urllib3 Response objects. Fixes occasional exceptions "ValueError: I/O operation on closed file." at shutdown.

Signed-off-by: Timothee Besset <ttimo@ttimo.net>

Author: Timothee Besset

docker/api/exec_api.py

@@ -173,4 +173,5 @@ def exec_start(self, exec_id, detach=False, tty=False, stream=False,
         if stream:
             return CancellableStream(output, res)
         else:
+            res.close()
             return output

docker/types/daemon.py

@@ -69,3 +69,5 @@ def close(self):
 
             sock.shutdown(socket.SHUT_RDWR)
             sock.close()
+
+        self._response.close()