tests: use sslutil.wrapserversocket()

tests: use sslutil.wrapserversocket()

Like the built-in HTTPS server, this code was using the ssl module
directly and only using TLS 1.0. Like the built-in HTTPS server,
we switch it to use sslutil.wrapserversocket() so it can follow better
practices.

--- a/tests/dummysmtpd.py	Tue Jul 12 23:12:03 2016 -0700
+++ b/tests/dummysmtpd.py	Wed Jul 13 20:41:07 2016 -0700
@@ -12,6 +12,8 @@
 
 from mercurial import (
     cmdutil,
+    sslutil,
+    ui as uimod,
 )
 
 def log(msg):
@@ -35,11 +37,10 @@
         if not pair:
             return
         conn, addr = pair
+        ui = uimod.ui()
         try:
             # wrap_socket() would block, but we don't care
-            conn = ssl.wrap_socket(conn, server_side=True,
-                                   certfile=self._certfile,
-                                   ssl_version=ssl.PROTOCOL_TLSv1)
+            conn = sslutil.wrapserversocket(conn, ui, certfile=self._certfile)
         except ssl.SSLError:
             log('%s ssl error\n' % addr[0])
             conn.close()