SPARK-1802. (Addendium) Audit dependency graph when Spark is built with -Pyarn

Following on a few more items from SPARK-1802 --

The first commit touches up a few similar problems remaining with the YARN profile. I think this is worth cherry-picking.

The second commit is more of the same for hadoop-client, although the fix is a little more complex. It may or may not be worth bothering with.

Author: Sean Owen <sowen@cloudera.com>

Closes #746 from srowen/SPARK-1802.2 and squashes the following commits:

52aeb41 [Sean Owen] Add more commons-logging, servlet excludes to avoid conflicts in assembly when building for YARN
(cherry picked from commit 4b31f4ec7efab8eabf956284a99bfd96a58b79f7)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>