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.
Hmm... this feels a little sub-optimal to me. For all others jars, the user has the option of either uploading them, or making them available on HDFS to avoid the cost of uploading them as part of every job. Perhaps the same should be done here?

Also, I don't expect you to know the answer to this question, but why aren't these jars included in the assembly jar when the Hive profile is enabled? That seems like it would be the best solution for everybody and would make this change unnecessary...