Copy pyspark and SparkR packages to latest release dir too
Copy pyspark and SparkR packages to latest release dir too

## What changes were proposed in this pull request?

Copy pyspark and SparkR packages to latest release dir, as per comment [here](https://github.com/apache/spark/pull/16226#discussion_r91664822)

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #16227 from felixcheung/pyrftp.

(cherry picked from commit c074c96dc57bf18b28fafdcac0c768d75c642cba)
Signed-off-by: Shivaram Venkataraman <ad63b47dfac1951bde2b661ba9fbbe123f686bee@cs.berkeley.edu>

kimoonkim/spark,Panos-Bletsos/spark-cost-model-optimizer,kimoonkim/spark,kimoonkim/spark,SnappyDataInc/spark,SnappyDataInc/spark,metamx/spark,Panos-Bletsos/spark-cost-model-optimizer,metamx/spark,ibm-research-ireland/sparkoscope,big-pegasus/spark,huang1900/spark,kimoonkim/spark,huang1900/spark,kimoonkim/spark,metamx/spark,metamx/spark,huang1900/spark,big-pegasus/spark,big-pegasus/spark,huang1900/spark,Panos-Bletsos/spark-cost-model-optimizer,SnappyDataInc/spark,huang1900/spark,big-pegasus/spark,Panos-Bletsos/spark-cost-model-optimizer,Panos-Bletsos/spark-cost-model-optimizer,SnappyDataInc/spark,huang1900/spark,ibm-research-ireland/sparkoscope,SnappyDataInc/spark,SnappyDataInc/spark,big-pegasus/spark,huang1900/spark,big-pegasus/spark,Panos-Bletsos/spark-cost-model-optimizer,kimoonkim/spark,ibm-research-ireland/sparkoscope,ibm-research-ireland/sparkoscope,SnappyDataInc/spark,ibm-research-ireland/sparkoscope,big-pegasus/spark,ibm-research-ireland/sparkoscope,metamx/spark,kimoonkim/spark,metamx/spark,metamx/spark,ibm-research-ireland/sparkoscope,Panos-Bletsos/spark-cost-model-optimizer