MAPREDUCE-5932. Provide an option to use a dedicated reduce-side shuffle log. Contributed by Gera Shegalov
(cherry picked from commit 03ab24aa01ffea1cacf1fa9cbbf73c3f2904d981)

Conflicts:

	hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/resources/mapred-default.xml