[SPARK-2267] Log exception when TaskResultGetter fails to fetch/deserialze task result

Note that this is only for branch-1.0 because master's been fixed.

Author: Reynold Xin <rxin@apache.org>

Closes #1202 from rxin/SPARK-2267 and squashes the following commits:

ce1b19b [Reynold Xin] [SPARK-2267] Log exception when TaskResultGetter fails to fetch/deserialize task result