Missing buffer size option for wsgi lead to 502

When deploying a Flask app to EBS (using the [tutorial](http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/create-deploy-python-flask.html)) one can face 502 HTTP status code when returning response with a size bigger than 4096.
```
invalid request block size: 4654 (max 4096)...skip
```

Apparently this script does not contemplate to configure the buffer-size option for WSGI.
After reading the doc about [configuration on EBS](http://docs.aws.amazon.com/elasticbeanstalk/latest/dg/create-deploy-python-container.html#create-deploy-python-custom-container-envprop) I am not sure if I can specify such an option without doing a hacky replace of the `uwsgi-start.sh` script and rerun it.

首先阅读 uwsgi-start.sh 脚本以及链接的 Elastic Beanstalk Python 容器配置文档。使用大于 4096 的响应重现 502，并跟踪 WSGI 选项的传递方式。当无需替换脚本即可通过受支持的 EBS 设置配置 buffer-size 选项时，即表示完成。

由索引模型根据 Issue 内容生成。