HDFS-7221. TestDNFencingWithReplication fails consistently. Contributed by Charles Lamb.

(cherry picked from commit ac56b0637e55465d3b7f7719c8689bff2a572dc0)
(cherry picked from commit 2d0996ae6d6bdfa01cff790f5ed7198d791de62b)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt