delete storage group after rebooting server

I tried to input these statements into CLI, and then closed and restart server. 

After that, I found out the whole storage group had been removed.

But actually I only removed one timeseries from storage group.  

```
set storage group to root.sg
create timeseries root.sg.d.s0 with datatype = int32, encoding=plain
delete timeseries root.sg.d.s0
create timeseries root.sg.d.s0 with datatype = int32, encoding=plain
create timeseries root.sg.d.s1 with datatype = int32, encoding=plain
insert into root.sg.d(timestamp, s0, s1) values(100,100,100)
flush
delete timeseries root.sg.d.s0
```