HADOOP-10852 Fix thread safety issues in NetgroupCache. (Benoy Antony)

(cherry picked from commit a095622f36c5e9fff3ec02b14b800038a81f6286)
HADOOP-11410. Make the rpath of libhadoop.so configurable (cmccabe)
(cherry picked from commit fb20797b6237054f3d16ff94a665cbad4cbe3293)
MAPREDUCE-6166. Reducers do not validate checksum of map outputs when fetching directly to disk. (Eric Payne via gera)

(cherry picked from commit af006937e8ba82f98f468dc7375fe89c2e0a7912)