Fixed fd leak from TCPServer

```
Leaked file descriptor: HTTPSProxyTest#test_https_proxy_ssl_connection: 8 : #<TCPServer:fd 8, AF_INET, 127.0.0.1, 63104>
```

test/net/http/test_https_proxy.rb

@@ -56,38 +56,39 @@ def test_https_proxy_ssl_connection
       omit 'autoload problem. see [ruby-dev:45021][Bug #5786]'
     end
 
-    tcpserver = TCPServer.new("127.0.0.1", 0)
-    ctx = OpenSSL::SSL::SSLContext.new
-    ctx.key = OpenSSL::PKey.read(read_fixture("server.key"))
-    ctx.cert = OpenSSL::X509::Certificate.new(read_fixture("server.crt"))
-    serv = OpenSSL::SSL::SSLServer.new(tcpserver, ctx)
+    TCPServer.open("127.0.0.1", 0) {|tcpserver|
+      ctx = OpenSSL::SSL::SSLContext.new
+      ctx.key = OpenSSL::PKey.read(read_fixture("server.key"))
+      ctx.cert = OpenSSL::X509::Certificate.new(read_fixture("server.crt"))
+      serv = OpenSSL::SSL::SSLServer.new(tcpserver, ctx)
 
-    _, port, _, _ = serv.addr
-    client_thread = Thread.new {
-      proxy = Net::HTTP.Proxy("127.0.0.1", port, 'user', 'password', true)
-      http = proxy.new("foo.example.org", 8000)
-      http.use_ssl = true
-      http.verify_mode = OpenSSL::SSL::VERIFY_NONE
-      begin
-        http.start
-      rescue EOFError
-      end
-    }
-    server_thread = Thread.new {
-      sock = serv.accept
-      begin
-        proxy_request = sock.gets("\r\n\r\n")
-        assert_equal(
-          "CONNECT foo.example.org:8000 HTTP/1.1\r\n" +
-          "Host: foo.example.org:8000\r\n" +
-          "Proxy-Authorization: Basic dXNlcjpwYXNzd29yZA==\r\n" +
-          "\r\n",
-          proxy_request,
-          "[ruby-core:96672]")
-      ensure
-        sock.close
-      end
+      _, port, _, _ = serv.addr
+      client_thread = Thread.new {
+        proxy = Net::HTTP.Proxy("127.0.0.1", port, 'user', 'password', true)
+        http = proxy.new("foo.example.org", 8000)
+        http.use_ssl = true
+        http.verify_mode = OpenSSL::SSL::VERIFY_NONE
+        begin
+          http.start
+        rescue EOFError
+        end
+      }
+      server_thread = Thread.new {
+        sock = serv.accept
+        begin
+          proxy_request = sock.gets("\r\n\r\n")
+          assert_equal(
+            "CONNECT foo.example.org:8000 HTTP/1.1\r\n" +
+            "Host: foo.example.org:8000\r\n" +
+            "Proxy-Authorization: Basic dXNlcjpwYXNzd29yZA==\r\n" +
+            "\r\n",
+            proxy_request,
+            "[ruby-core:96672]")
+        ensure
+          sock.close
+        end
+      }
+      assert_join_threads([client_thread, server_thread])
     }
-    assert_join_threads([client_thread, server_thread])
   end
 end if defined?(OpenSSL)