BUG/MINOR: http-fetch: Extract cookie value even when no cookie name

BUG/MINOR: http-fetch: Extract cookie value even when no cookie name

HTTP sample fetches dealing with the cookies (req/res.cook,
req/res.cook_val and req/res.cook_cnt) must be prepared to be called
without cookie name. For the first two, the first cookie value is
returned, regardless its name. For the last one, all cookies are counted.

To do so, http_extract_cookie_value() may now be called with no cookie
name (cookie_name_l set to 0). In this case, the matching on the cookie
name is ignored and the first value found is returned.

Note this patch also fixes matching on cookie values in ACLs.

This should be backported in all stable versions.