It looks like after the docs got converted to apt format in
HADOOP-8427, mvn site package -Pdist,docs no longer works. If you run mvn site or mvn site:stage by itself they work fine, its when you go to package it that it breaks.
The error is with broken links, here is one of them:
<link message="hadoop-common-project/hadoop-common/target/docs-src/src/documentation/content/xdocs/HttpAuthentication.xml (No such file or directory)" uri="HttpAuthentication.html">