This change attach the `request` to the exception under `response.value` where `response` is a `Failure` instance

I don't think we need another way to access the `request` from spider errbacks, there is another way already implemented that attaches `request` directly to `Failure` instance  at [scrapy/core/scraper.py#L139](https://github.com/scrapy/scrapy/blob/master/scrapy/core/scraper.py#L139)