raft: add Status interface

Status returns the current status of raft state machine.

etcdserver/server_test.go

@@ -1300,15 +1300,18 @@ func (n *nodeRecorder) Step(ctx context.Context, msg raftpb.Message) error {
 	n.Record(testutil.Action{Name: "Step"})
 	return nil
 }
+func (n *nodeRecorder) Status() raft.Status      { return raft.Status{} }
 func (n *nodeRecorder) Ready() <-chan raft.Ready { return nil }
 func (n *nodeRecorder) Advance()                 {}
 func (n *nodeRecorder) ApplyConfChange(conf raftpb.ConfChange) *raftpb.ConfState {
 	n.Record(testutil.Action{Name: "ApplyConfChange", Params: []interface{}{conf}})
 	return &raftpb.ConfState{}
 }
+
 func (n *nodeRecorder) Stop() {
 	n.Record(testutil.Action{Name: "Stop"})
 }
+
 func (n *nodeRecorder) Compact(index uint64, nodes []uint64, d []byte) {
 	n.Record(testutil.Action{Name: "Compact"})
 }