[Spark 1877] ClassNotFoundException when loading RDD with serialized objects

Updated version of #821

Author: Tathagata Das <tathagata.das1565@gmail.com>
Author: Ghidireac <bogdang@u448a5b0a73d45358d94a.ant.amazon.com>

Closes #835 from tdas/SPARK-1877 and squashes the following commits:

f346f71 [Tathagata Das] Addressed Patrick's comments.
fee0c5d [Ghidireac] SPARK-1877: ClassNotFoundException when loading RDD with serialized objects