t1800: add test to verify hook execution ordering

t1800: add test to verify hook execution ordering

There is a documented expectation that configured hooks are
run before the hook from the hookdir. Add a test for it.

While at it, I noticed that `git hook list -h` runs twice
in the `git hook usage` test, so remove one invocation.

Suggested-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>