describe tests: refactor away from glob matching

describe tests: refactor away from glob matching

Change the glob matching via a "case" statement to a "test_cmp" after
we've stripped out the hash-specific g<hash-abbrev>
suffix. 5312ab11fbf (Add describe test., 2007-01-13).

This means that we can use test_cmp to compare the output. I could
omit the "-8" change of e.g. "A-*" to "A-8-gHASH", but I think it
makes sense to test that here explicitly. It means you need to add new
tests to the bottom of the file, but that's not a burden in this case.

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