[SPARK-4618][SQL] Make foreign DDL commands options case-insensitive

Using lowercase for ```options``` key to make it case-insensitive, then we should use lower case to get value from parameters.
So flowing cmd work
```
      create temporary table normal_parquet
      USING org.apache.spark.sql.parquet
      OPTIONS (
        PATH '/xxx/data'
      )
``` 
>You mean like this?

No, I mean you should construct the case insensitive map in the parser just like now.  The only change is to pass it into createRelation without changing the signature of the createRelation function.