raft: port from etcd. (#745)
raft: port from etcd. (#745)

raft: truncateAndAppend no need the value of 'after' with subbing one
BusyJay/tikv,BusyJay/tikv,c4pt0r/tikv,BusyJay/tikv,BusyJay/tikv,pingcap/tikv,pingcap/tikv