bpo-30199: test_ssl closes all asyncore channels (#1381) (#1408)

AsyncoreEchoServer of test_ssl now calls
asyncore.close_all(ignore_all=True) to ensure that
asyncore.socket_map is cleared once the test completes, even if
ConnectionHandler was not correctly unregistered.

Fix the following warning:

Warning -- asyncore.socket_map was modified by test_ssl
  Before: {}
  After:  {6: <test.test_ssl.AsyncoreEchoServer.EchoServer.ConnectionHandler>}
(cherry picked from commit 1dae7450)

Lib/test/test_ssl.py

@@ -1955,6 +1955,8 @@ else:
             self.join()
             if support.verbose:
                 sys.stdout.write(" cleanup: successfully joined.\n")
+            # make sure that ConnectionHandler is removed from socket_map
+            asyncore.close_all(ignore_all=True)
 
         def start(self, flag=None):
             self.flag = flag