reduce etcd MTTR on process restart

This task adds support for setting socket options SO_REUSEADDR and SO_REUSEPORT to etcd listeners via ListenConfig. These options give the flexibility to cluster admins who wish to more explicit control of these features. What we have found is during etcd process restart there can be a considerable time waiting for the port to release as it is held open by TIME_WAIT which on many systems is 60s.