Raftable client always tries to connect dead node.

[kelvich]

Setup cluster of 3 nodes, pgbench -i, kill first one, pgbench of node2 (or just commit rw tx in connection):

WARNING:  raftable client: trying [0] localhost:6543
WARNING:  raftable client: connect timed out
WARNING:  raftable client: could not connect
WARNING:  raftable client: connect_leader() failed
WARNING:  raftable query failed after 452 ms
progress: 1.0 s, 270.0 tps, lat 3.688 ms stddev 27.804
WARNING:  raftable client: trying [2] localhost:6545