raft/rawnode.go
func (rn *RawNode) Campaign() error {
	return rn.raft.Step(pb.Message{
		Type: pb.MsgHup,
	})
}
func (rn *RawNode) Campaign() error {
	return rn.raft.Step(pb.Message{
		Type: pb.MsgHup,
	})
}
// Campaign causes this RawNode to transition to candidate state.