Copy down files (Part 4)

In the fourth part of our series we look at how to automatically join the three other virtual machines to the contoso.com domain, again using an custom extension in our Azure Resource Manager template.
The series landing page on "Full of I.T.": https://aka.ms/AZInfraLabBlog
"The Links" document: https://aka.ms/AZInfraLabLinks
Kevin's GitHub lab base repository https://aka.ms/AZInfraLabBase