Description
This was a suggestion by rxin over one of the dev list discussion : http://apache-spark-developers-list.1001551.n3.nabble.com/Project-not-preserving-child-partitioning-td19417.html
I think this is very risky because preserving output partitioning should not be a property of UnaryNodeExec (e.g. exchange). It would be better (safer) to move the output partitioning definition into each of the operator and remove it from UnaryExecNode.