[SPARK-2710] [SQL] Build SchemaRDD from a JdbcRDD with MetaData

SPARK-2710 Build SchemaRDD from a JdbcRDD with MetaData

and a small bug fix on JdbcRDD, line 109
it seems conn will never be closed


http://db.apache.org/derby/papers/DerbyTut/embedded_intro.html

" A clean shutdown always throws SQL exception XJ015, which can be ignored. "