Pin _artifactsLocation to a git tag

[ItalyPaleAle]

Currently, the default value for _artifactsLocation is https://raw.githubusercontent.com/Azure/LAMP/master/.

We should start tagging "versions" of this template, possibly following semver, and "pin" the version to a git tag.

This is important because if customers deploy the template and we make some changes to the bash scripts (not the templates themselves) in master, then VMs in the VMSS would always pick up the scripts from master, which might break the deployment.

(A second thing we should do is to recommend customers to copy the scripts in their storage accounts too)