test_gem_remote_fetcher.rb: terminate watcher

* test/rubygems/test_gem_remote_fetcher.rb (stop_servers):
  terminate timeout watcher thread to fix thread leak.  re-apply
  r53439.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53777 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/rubygems/test_gem_remote_fetcher.rb

@@ -924,6 +924,8 @@ def stop_servers
         @ssl_server_thread.kill.join
         @ssl_server_thread = nil
       end
+      timeout = WEBrick::Utils::TimeoutHandler
+      timeout.terminate if defined?(timeout.terminate)
     end
 
     def normal_server_port