MAPREDUCE-5454. TestDFSIO fails intermittently on JDK7 (Karthik Kambatla via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1513377 13f79535-47bb-0310-9956-ffa450edef68