Sometimes raft deadlocks

[LK4D4]

We saw it on ci: on 3-machine cluster creation sometimes nodes can't decide who is leader and hang on term 2 forever:

    node 1: term 2, leader 1
    node 2: term 2, leader 1
    node 3: term 2, leader 3

It appears on CI pretty often I think because of limited CPU time, I saw it on my machine as well when used smaller raft tick.
I dunno, maybe will be fixed by #131

[abronan]

It's just a race on adding new nodes, this might indeed be fixed by mechanisms introduced in #131. The problem is that etcd rejects configuration changes submitted concurrently. One will pass, the other will get rejected. Thus node 3 tries to join but node 2 is still in the process of joining. node 3 join gets rejected and it ends up being alone thus electing itself as the leader.

[aaronlehmann]

I think this is fixed by the combination of #131 and #237. Okay to close?