rev-list simplify tests: don't ignore "git" exit code

rev-list simplify tests: don't ignore "git" exit code

Change a fragile test pattern introduced in 65347030590 (Topo-sort
before --simplify-merges, 2008-08-03) to check the exit code of both
"git name-rev" and "git log".

This test as a whole would fail under SANITIZE=leak, but we'd pass
several "failing" tests due to hiding these exit codes before we'd
spot git dying with abort(). Now we'll instead spot all of the
failures.

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