Introduce cookie_private for LocalRequest

[madeindjs]

Feature request

Currently to run local test with cookie you should use cookie method.

Example

#[test]
fn should_not_redirect_on_get_new_recipe() {
    let client = Client::new(rocket()).unwrap();
    let request = client.get("/recipes/new").cookie(
        Cookie::new("user_id", "1"),
    );
    let response = request.dispatch();
    assert_eq!(response.status(), Status::Ok);
}

But nothing exists to create private cookie like add_private for rocket::http::Cookies.

What do you think of?

[madeindjs]

I just saw this opening Pull Request #487

[SergioBenitez]

Duplicate of #368.