After we have determinted the root URL, create a download script from a given jinja2 template. This is added to the file list at the root and uploaded with the other files. Generated index files are given a new flag so they can be differentiated. This is an impelementation of Iea8abd4cd71ece26b51335642f73bd2e544c42dd for the swift-upload role. Change-Id: I98c80f657f38c5e1ed5f28e5d36988a3429ad1f8