tests: rename a test having to do with shallow submodules

Rename the t5614-clone-submodules.sh test to t5614-clone-submodules-shallow.sh. It's not a general test of submodules, but of shallow cloning in relation to submodules. Move it to create another similar t56*-clone-submodules-*.sh test. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>