test-lib: set LSAN_OPTIONS to abort by default

test-lib: set LSAN_OPTIONS to abort by default

We already set ASAN_OPTIONS to abort if it finds any errors.
As we start to experiment with LSAN, the leak sanitizer,
it's convenient if we give it the same treatment.

Note that ASAN is actually a superset of LSAN and can do the
leak detection itself. So this only has an effect if you
specifically build with "make SANITIZE=leak" (leak detection
but not the rest of ASAN). Building with just LSAN results
in a build that runs much faster. That makes the
build-test-fix cycle more pleasant.

In the long run, once we've fixed or suppressed all the
leaks, it will probably be worth turning leak-detection on
for ASAN and just using that (to check both leaks _and_
memory errors in a single test run). But there's still a lot
of work before we get there.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>