message: Improve core test of gethostbyname
diff: using swoole::Coroutine;
  using swoole::coroutine::System;
  -TEST(coroutine_gethostbyname, resolve_with_cache)
  +TEST(coroutine_gethostbyname, resolve_cache)
  {
  coro_test([](void *arg)
  {
  System::set_dns_cache_capacity(10);
  -
  std::string addr1 = System::gethostbyname("www.baidu.com", AF_INET);
  ASSERT_NE(addr1, "");
  -
  - int64_t start = swTimer_get_absolute_msec();
  -
  + int64_t with_cache = swTimer_get_absolute_msec();
  for (int i = 0; i < 100; ++i)
  {
  std::string addr2 = System::gethostbyname("www.baidu.com", AF_INET);
  ASSERT_EQ(addr1, addr2);
  }
  + with_cache = swTimer_get_absolute_msec() - with_cache;
  - ASSERT_LT(swTimer_get_absolute_msec() - start, 5);
  - });
  -}
  -
  -TEST(coroutine_gethostbyname, resolve_without_cache)
  -{
  - coro_test([](void *arg)
  - {
  System::set_dns_cache_capacity(0);
  -
  - std::string addr1 = System::gethostbyname("www.baidu.com", AF_INET);
  - ASSERT_NE(addr1, "");
  -
  - int64_t start = swTimer_get_absolute_msec();
  -
  + int64_t without_cache = swTimer_get_absolute_msec();
  for (int i = 0; i < 5; ++i)
  {
  std::string addr2 = System::gethostbyname("www.baidu.com", AF_INET);
  ASSERT_NE(addr2, "");
  }
  + without_cache = swTimer_get_absolute_msec() - without_cache;
  - ASSERT_GT(swTimer_get_absolute_msec() - start, 3);
  + ASSERT_GT(without_cache, with_cache);
  });
  }
  