[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


line 60 there is a
private var schema: Seq[(String, Int, Boolean)] = null
is it works in scala? in java it should be ok