A suitable Hadoop client for running tasks from Docker containers

This supports our old and new Hadoop clusters. The approach uses two separate entrypoint scripts to set up the different versions.

Hadoop 3 command can be run like this:

$ docker-compose run client hadoop fs -ls /

This depends on the h3nn and h3rm hosts being set up in DNS.

$ docker-compose run --entrypoint /entrypoint-h020.sh  client hadoop fs -ls /

The configuration uses hard-coded IP addresses the Hadoop 0.20 Namenode and Job Tracker.