Pass route_name from use_route on path_for [4.2.0 regression]

engines need it to be able to get a proper request uri on tests, the
value was lost in https://github.com/rails/rails/commit/212057b912627b9c4056f911a43c83b18ae3ab34

will look into adding a regression test

// @tenderlove 
Actually, where is the `:use_route` key actually being set? It must be coming either from the `@controller.url_options` call or it's in `parameters` and neither of those seem likely candidates.