Better async startup / shutdown hooks

[tj]

currently the events fire, but they do not allow the shutdown to halt until cleanup is complete, removing files, sockets etc

[jeffv]

Was going to add this issue, but I see you've added it yourself. We've been running cluster in production for quite a while and those sockets can really pile up.

[tj]

it's a bit of a tough call, because if you defer the exit without some kind of timeout whatever task(s) may never finish, which is definitely far from ideal