raft: add node should reset the pendingConf state

After add node conf proposed twice with the same node id, the pending state is not reset because
the addNode returned without setting the pending state at the second
time and the pending state will always be true unless other conf changed. During this we
can not add any new node because the propose will be ignored since the
pending state is true.

raft/raft.go

@@ -813,6 +813,7 @@ func stepLeader(r *raft, m pb.Message) {
 		for i, e := range m.Entries {
 			if e.Type == pb.EntryConfChange {
 				if r.pendingConf {
+					r.logger.Infof("propose conf %s ignored since pending unapplied configuration", e.String())
 					m.Entries[i] = pb.Entry{Type: pb.EntryNormal}
 				}
 				r.pendingConf = true
@@ -1145,6 +1146,7 @@ func (r *raft) promotable() bool {
 }
 
 func (r *raft) addNode(id uint64) {
+	r.pendingConf = false
 	if _, ok := r.prs[id]; ok {
 		// Ignore any redundant addNode calls (which can happen because the
 		// initial bootstrapping entries are applied twice).
@@ -1152,7 +1154,6 @@ func (r *raft) addNode(id uint64) {
 	}
 
 	r.setProgress(id, 0, r.raftLog.lastIndex()+1)
-	r.pendingConf = false
 }
 
 func (r *raft) removeNode(id uint64) {