bpo-40275: Avoid importing socket in test.support (GH-19603)

* Move socket related functions from test.support to socket_helper.
* Import socket, nntplib and urllib.error lazily in transient_internet().
* Remove importing multiprocess.
diff --git a/Lib/test/test_wsgiref.py b/Lib/test/test_wsgiref.py
index 6af4514..4bf5d39 100644
--- a/Lib/test/test_wsgiref.py
+++ b/Lib/test/test_wsgiref.py
@@ -1,5 +1,6 @@
 from unittest import mock
 from test import support
+from test.support import socket_helper
 from test.test_httpservers import NoLogRequestHandler
 from unittest import TestCase
 from wsgiref.util import setup_testing_defaults
@@ -263,7 +264,7 @@
         class WsgiHandler(NoLogRequestHandler, WSGIRequestHandler):
             pass
 
-        server = make_server(support.HOST, 0, app, handler_class=WsgiHandler)
+        server = make_server(socket_helper.HOST, 0, app, handler_class=WsgiHandler)
         self.addCleanup(server.server_close)
         interrupted = threading.Event()