Update to Latest DataStax Template

https://github.com/Azure/azure-quickstart-templates/tree/master/datastax-enterprise-marketplace
https://github.com/Azure/azure-quickstart-templates/tree/master/datastax-enterprise
https://github.com/Azure/azure-quickstart-templates/tree/master/datastax-on-ubuntu
### Issue Details

The three DataStax templates here are rather old. I've been working with Azure engineering on a different version here: https://github.com/DSPN/azure-resource-manager-dse

Can we come up with a strategy to keep this template up to date? I can think of a variety of options.

Feel free to send me a note to discuss.

-Ben Lackey

Compare the three referenced template directories—datastax-enterprise-marketplace, datastax-enterprise, and datastax-on-ubuntu—with the DSPN/azure-resource-manager-dse repository. Start by identifying differences in the existing Azure templates and the proposed version, then document an agreed strategy for keeping them current. Done means the maintenance approach is decided and the templates are updated accordingly.

Written by the indexing model from the issue text.