MINOR: pools: always evict oldest objects first in pool_evict_from_local_cache()

MINOR: pools: always evict oldest objects first in pool_evict_from_local_cache()

For an unknown reason, despite the comment stating that we were evicting
oldest objects first from the local caches, due to the use of LIST_NEXT,
the newest were evicted, since pool_put_to_cache() uses LIST_INSERT().

Some tests on 16 threads show that evicting oldest objects instead can
improve performance by 0.5-1% especially when using shared pools.