docker-compose.yaml sets namenode directory wrong causing datanode failures on restart

It is possible to reproduce issue https://issues.apache.org/jira/browse/HDFS-17307 also using the docker-compose.yaml in branch docker-hadoop-2.

Beeing unsure how to proceed, considering this issue applies to a different branch, I created a duplicated issue. Please let me know if this was not the correct way to proceed.