Go system tests: Close proxy and stub at the end of a test.

mojo/go/tests/regression_test.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package tests
 
 import (
         "fmt"
         "sync"
         "testing"
@@ skipping 32 matching lines @@
                         }
                 }()
                 if err := proxy.WithoutParameterAndEmptyResponse(); err != nil {
                         t.Fatalf("error sending request: %v", err)
                 }
                 v.mu.Lock()
                 if !v.methodCalled {
                         t.Fatal("proxy returned from the call before the stub sent the response")
                 }
                 v.mu.Unlock()
+                proxy.Close_Proxy()
+                stub.Close()
         }
 }