tests: make the telnet server shut down a socket gracefully

- test 1452 failed occasionally with ECONNRESET errnos in curl when the
  server closed the connection in an unclean state.

Closes #10509

tests/negtelnetserver.py

@@ -29,7 +29,9 @@ from __future__ import (absolute_import, division, print_function,
 import argparse
 import logging
 import os
+import socket
 import sys
+import time
 
 from util import ClosingFileHandler
 
@@ -90,7 +92,7 @@ class NegotiatingTelnetHandler(socketserver.BaseRequestHandler):
             neg.send_wont("NAWS")
 
             # Get the data passed through the negotiator
-            data = neg.recv(1024)
+            data = neg.recv(4*1024)
             log.debug("Incoming data: %r", data)
 
             if VERIFIED_REQ.encode('utf-8') in data:
@@ -109,6 +111,12 @@ class NegotiatingTelnetHandler(socketserver.BaseRequestHandler):
                 log.debug("Sending %r", response_data)
                 self.request.sendall(response_data)
 
+            # put some effort into making a clean socket shutdown
+            # that does not give the client ECONNRESET
+            self.request.settimeout(0.1)
+            self.request.recv(4*1024)
+            self.request.shutdown(socket.SHUT_RDWR)
+
         except IOError:
             log.exception("IOError hit during request")