A RaftAcotor(Leader) could mis-deliver a ReplicationSucceeded message to a different entity

[xirc]

Situation

1. RaftActor on node A starts a replication for entity X with index=5 (for example).
2. RaftActor on node A becomes a follower before the replication completes for some reason.
   • RaftActor on node B is the leader now.
   • The new leader has a Raft log with lastLogIndex=3 (for example).
3. RaftActor on node B starts a new replication.
   • This replication contains a log entry (index=5, but an event is for entity Y), for example.
4. RaftActor on node A receives AppendEntries from RaftActor on node B
   • This receiving truncates the log entry (index=5, an event for entity X) because the entry is conflicted.
5. RaftActor on node B becomes a follower before the replication completes for some reason.
   • RaftActor on node A is the leader again.
6. RaftActor on node A completes the ongoing replication
7. RaftActor on node A will send a ReplicationSucceeded message containing the log entry (index=5, the event is for entity Y) to entity X.
   • It is because LeaderData.clients associates a ClientContext for entity X with index=5.

Possible Solution

Similar to #155