[SPARK-4436][SPARK-3624][BUILD] Debian packaging fixes

This makes the Spark jar as well as the datanucleus jars (and anything else in lib_managed/jars) available in the debian package at spark/lib.  In addition to allowing HiveContext to work with a deb package built using -Phive, this incorporates the clean&simple-but-not-backward-compatible fix for SPARK-3624, which has been needed since Spark 1.0.0.

@JoshRosen @tzolov @pwendell @andrewor14