t5551: handle v2 protocol in cookie test

t5551: handle v2 protocol in cookie test

After making a request, we check that it stored the expected cookies.
This depends on the protocol version, because the cookies we store
depend on the exact requests we made (and for ls-remote, v2 will always
hit /git-upload-pack to get the refs, whereas v0 is happy with the
initial ref advertisement).

As a result, hardly anybody runs this test, as you'd have to manually
set GIT_TEST_PROTOCOL_VERSION=0 to do so.

Let's teach it to handle both protocol versions. One way to do this
would be to make the expectation conditional on the protocol used. But
there's a simpler solution. The reason that v0 doesn't hit
/git-upload-pack is that ls-remote doesn't fetch any objects. If we
instead do a fetch (making sure there's an actual object to grab), then
both v0 and v2 will hit the same endpoints and set the same cookies.

Note that we do have to clean up our new tag here; otherwise it confuses
the later "clone 2,000 tags" test.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>