fix graceful restart and add unit test

tests/graceful_cli.py

@@ -0,0 +1,18 @@
+#!/usr/bin/python
+
+import socket
+import socks
+import time
+
+
+SERVER_IP = '127.0.0.1'
+SERVER_PORT = 8001
+
+
+if __name__ == '__main__':
+    s = socks.socksocket()
+    s.set_proxy(socks.SOCKS5, SERVER_IP, 1081)
+    s.connect((SERVER_IP, SERVER_PORT))
+    s.send(b'test')
+    time.sleep(30)
+    s.close()