bundle-uri client: add helper for testing server

bundle-uri client: add helper for testing server

Add a 'test-tool bundle-uri ls-remote' command. This is a thin wrapper
for issuing protocol v2 "bundle-uri" commands to a server, and to the
parsing routines in bundle-uri.c.

In the "git clone" case we'll have already done the handshake(),
but not here. Add an extra case to check for this handshake in
get_bundle_uri() for ease of use for future callers.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>