HADOOP-9906. Move HAZKUtil to o.a.h.util.ZKUtil and make inner-classes public (Karthik Kambatla via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1518310 13f79535-47bb-0310-9956-ffa450edef68