These may conflict with the classes already in the NM. We shouldn't
be repackaging them.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #4820 from vanzin/SPARK-6070 and squashes the following commits:

871b566 [Marcelo Vanzin] The "d'oh how didn't I think of it before" solution.
3cba946 [Marcelo Vanzin] Use profile instead, so that dependencies don't need to be explicitly listed.
7a18a1b [Marcelo Vanzin] [SPARK-6070] [yarn] Remove unneeded classes from shuffle service jar.