TAJO-1249: Tajo Should Check File Format is allowed.

Currently Tajo just show NullPointException when can't understand file format
```c
default> create external table table1 ( id int, name text, score float, type text, mytime int, mytime2 date) using TEXT1 location 'file:/Users/charsyam/tajo/table';
ERROR: java.lang.NullPointerException
```
It is better to return using verficationstate