This is similar to
HDFS-5624 (Add tests for ACLs in combination with viewfs)
We should verify that XAttr operations work properly with viewfs, and that XAttr commands are routed to the correct namenode in a federated deployment.
Also, we should make sure that the behavior of XAttr commands on internal dirs is consistent with other commands. For example, setPermission will throw the readonly AccessControlException for paths above the root mount entry.