The cluster-dns images' scripts are only working with Python 2.
Considering that Python 2 support will be dropped in 2020, it
would be a good idea to transition towards Python 3 support.
This commit the cluster-dns Python scripts to work on both
Python versions.
the command in example should be straightforward asap, user just
do copy and paste to move on. This change is align with spark
example to set CLUSTER_NAME and USER_NAME, refer to below link for
the details:
https://github.com/kubernetes/examples/tree/master/staging/spark