Performs a right outer region join between two RDDs.
The 'left' side of the join
The 'right' side of the join
An RDD of pairs (Option[x], y), where the optional x value is from baseRDD, y is from joinedRDD, and the region corresponding to x overlaps the region corresponding to y. If there are no keys in the baseRDD that overlap a given key (y) from the joinedRDD, x will be None.