"fix go client get params channel return bug"

[dzhwinter]

In client.go:SendGrads:

for err := range errCh {
		if err != nil {
			return err
		}

		recv++
		if recv == len(grads) {
			break
		}
	}

should not return err, or the function will stop waiting for other goroutines to finish, causing unexpected errors, and should log the error.

@typhoonzero found that return error immediately will lead to some goroutine get out of control, this PR is a fix.

[typhoonzero]

LGTM! Merge after @helinwang's review!

[helinwang]

Thanks! one comment.
It's good to log the errors, but I don't get why there is problem before?
The result channel is buffered channel rCh := make(chan result, len(names)), I don't get why go-rountine will never be released?

[helinwang]

Can we log all the errors?

[dzhwinter]

I thought they are the same errors because there is only one source of error.

[dzhwinter]

@typhoonzero 认为原来的代码中buffered channel在收到第一个err后，return将直接返回，该函数运行结束。由于errCh所在函数已经消失，其余的goroutine全部失控了。

  errCh := make(chan error, len(grads))
  for _, g := range grads {
    go func(g Gradient) {
      err := c.pservers[c.partition(g.Name)].Call("Service.SendGrad", g, nil)
      errCh <- err
    }(g)
  }

要不，我写个程序测试一下？

[helinwang]

@dzhwinter 嗯辛苦测试一下吧～我理解这里errCh即使生成他的function返回，因为被其他go-rountine引用，是不会被释放的，所以不会有问题。也可能是我理解错了。

[luotao1]

感谢您给PaddlePaddle贡献代码。由于Paddle V1/V2版本已不再维护，相关代码也已从develop分支上删除，因此关闭您的PR，欢迎您向Paddle最新版-Fluid贡献代码。
Thanks for contributing to PaddlePaddle! Since V1/V2 will not be maintained anymore, and related codes have been deleted from develop branch as well, we close this PR. Welcome to contribute to Fluid——the latest version of PaddlePaddle.