Tell the Docker container to use 'localhost' as the hostname, so that
any Hadoop-generated job tracking urls are usable from a Hadoop client
running on the same host (relies on pre-configured port mappings)
Don't format the namenode (as user root), since it's done as user hdfs
from within hdfs-create-dirs
Modifications to allow a Docker volume to be used for the datanode (with
an example run script)