raft/storage.go
func (ms *MemoryStorage) SetHardState(st pb.HardState) error {
	ms.Lock()
	defer ms.Unlock()
	ms.hardState = st
	return nil
}
func (ms *MemoryStorage) SetHardState(st pb.HardState) error {
	ms.Lock()
	defer ms.Unlock()
	ms.hardState = st
	return nil
}
// SetHardState saves the current HardState.