[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


Hmm, yeah good question... Perhaps @koeninger, who wrote the original test, could enlighten us?