text-frontend VCL: grep Orig-Cookie for GeoIP, not (just) Cookie

We want to perform geolocation if and only if the GeoIP cookie is not already
set on the incoming client request, but at the point where we perform the
check, the Cookie header has been squirreled away in Orig-Cookie to trick
Varnish into serving certain types of cookied requests from the cache.

So why check req.http.Cookie at all? Simply because at some point in the future
someone will surely move things around and break the universe, so we might as
well be resilient.

Change-Id: I7cd1ec63a457c29d94646a0fd33aa7b5a590dc6b