proc-receive hook tests: use "test_hook" instead of "write_script"

proc-receive hook tests: use "test_hook" instead of "write_script"

Change the t5411/*.sh tests to use the test_hook helper instead of
"write_script". Unfortunately these tests do the setup and test across
different test_expect_success blocks, so we have to use
--clobber (implying --setup) for these.

Let's change those that can use a quoted here-doc to do so while we're
at it.

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