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_xmlrpc.py b/Lib/test/test_xmlrpc.py
index e5c3496..f68af52 100644
--- a/Lib/test/test_xmlrpc.py
+++ b/Lib/test/test_xmlrpc.py
@@ -15,6 +15,7 @@
 import io
 import contextlib
 from test import support
+from test.support import socket_helper
 from test.support import ALWAYS_EQ, LARGEST, SMALLEST
 
 try:
@@ -334,7 +335,7 @@
             server.handle_request()  # First request and attempt at second
             server.handle_request()  # Retried second request
 
-        server = http.server.HTTPServer((support.HOST, 0), RequestHandler)
+        server = http.server.HTTPServer((socket_helper.HOST, 0), RequestHandler)
         self.addCleanup(server.server_close)
         thread = threading.Thread(target=run_server)
         thread.start()