relay: keep_running is no longer global
relay: keep_running is no longer global

All consumers now keep their own state, so we can properly control the
order of shutdown.

grobian/carbon-c-relay,zzl0/carbon-c-relay,rtoma/carbon-c-relay,tjamesturner/carbon-c-relay,tjamesturner/carbon-c-relay,piotr1212/carbon-c-relay,zzl0/carbon-c-relay,Skyscanner/carbon-c-relay,grobian/carbon-c-relay,lyft/carbon-c-relay,grobian/carbon-c-relay,piotr1212/carbon-c-relay,rtoma/carbon-c-relay,Skyscanner/carbon-c-relay,lyft/carbon-c-relay,piotr1212/carbon-c-relay,lyft/carbon-c-relay,piotr1212/carbon-c-relay