TAJO-1030: Not supported JDBC APIs should return empty results instead of Exception

Thank you for checking. Keep going.

I misunderstood due to the following statements (http://www.postgresql.org/docs/9.2/static/ddl-schemas.html).

```In the previous sections we created tables without specifying any schema names. By default such tables (and other objects) are automatically put into a schema named "public". Every new database contains such a schema.```