aztk spark init --python flag not working as expected

[jiata]

When i run aztk spark init --python, the docker_repo is not updated to the python docker image.

This flag should also enable jupyter and jupyter lab automatically.

[jiata]

we should also update the python wiki when this is revolved.

[jafreck]

The --python flag should work since #486. The wiki still needs to be updated, though. Thanks for finding this.