tests: extend "test_hook" for "rm" and "chmod -x", convert "$HOOK"

tests: extend "test_hook" for "rm" and "chmod -x", convert "$HOOK"

Extend the "test_hook" function to take options to disable and remove
hooks. Using the wrapper instead of getting the path and running
"chmod -x" or "rm" will make it easier to eventually emulate the same
behavior with config-based hooks.

Not all of these tests need that new mode, but since the rest are
either closely related or use the same "$HOOK" pattern let's convert
them too.

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