HADOOP-9221. Convert remaining xdocs to APT. (Andy Isaacson via tgraves)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1440570 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'branch-0.23' of github.com:griddynamics/yhadoop-common into branch-0.23-gd
Merge branch 'branch-0.23-gd' of github.com:griddynamics/yhadoop-common into fb-HADOOP-9170-branch-0.23-gd