异步请求网络图片（当使用第三方加载图片卡顿的时候可以使用这个方法

let urlImage = NSURL(string: _model.image!)

let request = NSURLRequest(URL: urlImage!)

NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) { (requst, data, error) -> Void in

let image = UIImage(data: data!)

self.imageView1.image = image

}