* Trying to simultaneously resolving conflicts at several nodes creates new conflicts.
Therefore the leader resolves conflicts to limit divergence. To avoid overload there
is also a configurable rate limit of how many conflicts that are handled by second.
* Netty blocks when sending to broken connections. ClusterHeartbeatSender actor
isolates sending to different nodes by using child workers for each target
address and thereby reduce the risk of irregular heartbeats to healty
nodes due to broken connections to other nodes.
