mktag tests: parse out options in helper

mktag tests: parse out options in helper

Change check_verify_failure() helper to parse out options from
$@. This makes it easier to add new options in the future. See
06ce79152be (mktag: add a --[no-]strict option, 2021-01-06) for the
initial implementation.

Let's also replace "" quotes with '' for the test body, the varables
we need are eval'd into the body, so there's no need for the quoting
confusion.

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