SPARK-2624 add datanucleus jars to the container in yarn-cluster

If `spark-submit` finds the datanucleus jars, it adds them to the driver's classpath, but does not add it to the container.

This patch modifies the yarn deployment class to copy all `datanucleus-*` jars found in `[spark-home]/libs` to the container.
Ah, I see what you're doing. You're manually adding all the datanucleus jars to the classpath by propagating the config. I wonder if, for the sake of simplicity, piggybacking on `cachedSecondaryJarLinks` is good enough.