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/ssl_servers.py b/Lib/test/ssl_servers.py
index 2e7e235..a4bd745 100644
--- a/Lib/test/ssl_servers.py
+++ b/Lib/test/ssl_servers.py
@@ -9,10 +9,11 @@
     SimpleHTTPRequestHandler, BaseHTTPRequestHandler)
 
 from test import support
+from test.support import socket_helper
 
 here = os.path.dirname(__file__)
 
-HOST = support.HOST
+HOST = socket_helper.HOST
 CERTFILE = os.path.join(here, 'keycert.pem')
 
 # This one's based on HTTPServer, which is based on socketserver