test-lib functions: add an --annotated option to "test_commit"

test-lib functions: add an --annotated option to "test_commit"

Add an --annotated option to test_commit to create annotated tags. The
tag will share the same message as the commit, and we'll call
test_tick before creating it (unless --notick) is provided.

There's quite a few tests that could be simplified with this
construct. I've picked one to convert in this change as a
demonstration.

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