Improved connection draining with small number of connections. Closing up to 32 connections might be too aggressive if worker_connections is set to a comparable number (and/or there are only a small number of reusable connections). If an occasional connection shorage happens in such a configuration, it leads to closing all reusable connections instead of gradually reducing keepalive timeout to a smaller value. To improve granularity in such configurations we now close no more than 1/8 of all reusable connections at once. Suggested by Joel Cunningham.