add retry support for socket timeout

[kaisecheng]

This plugin doesn't retry when SocketTimeoutException happens, such as read time out. Other plugins like http-output can catch this exception and customize the response code to retry.

This feature request is to add the same retry support from http-output to this plugin.
If possible, bring the same features to http-filter, or even better, bring it to mixin-http_client, so all http related plugins share the same source and features