latch_destroy() and fiber_cond_destroy() are basically no-op. All they
do is check that latch/cond is not used. When a global latch or cond
object is destroyed at exit, it may still have users and this is OK as
we don't stop fibers at exit. In vinyl this results in the following
false-positive assertion failures:

  src/latch.h:81: latch_destroy: Assertion `l->owner == NULL' failed.

  src/fiber_cond.c:49: fiber_cond_destroy: Assertion `rlist_empty(&c->waiters)' failed.

Remove "destruction" of vy_log::latch to suppress the first one. Wake up
all fibers waiting on vy_quota::cond before destruction to suppress the
second one. Add some test cases.

Closes #3412