Rancher template opens Docker daemon to the public internet

[docker-rancher](https://github.com/Azure/azure-quickstart-templates/tree/master/docker-rancher)

### Issue Details
On my MSDN subscription I've started with the docker-rancher template to test out if Rancher can be of use for our organization. The template is easy to install and use. However after 5 days I noticed a large amount of my Azure credits where spend on outgoing traffic. This was strange because Rancher should have been in a idle state... After investigating the VM using ssh I noticed a connection has been made to China from my VM which I definitely didn't do.

If you look at the template it makes use of the [Docker extension](https://github.com/Azure/azure-docker-extension) and it's is configured in such a way that it doesn't require certificates to be used. The Network Security Group allows traffic on port 2375 from the public internet which exposes the VM.

Please change to template to make it secure by default. There are bad people which are scrapping IP's to check for unprotected Docker daemons to run their malicious workloads.

### Repro steps
1. Install the template
2. Connect to the docker daemon

Start in the docker-rancher template linked in the issue and inspect its Docker extension configuration and Network Security Group rules, especially public access to port 2375. Reproduce the exposure by following the listed installation and connection steps; done means the deployed template no longer exposes an unauthenticated Docker daemon to the public internet.

Written by the indexing model from the issue text.