StoreFront upgrade fails ""The process cannot access the file 'C:\inetpub\wwwroot\Citrix\<store name>\web.config' because it is being used by another process."

In the MSI logs under C:\windows\temp\storefront we see the following exception: "The process cannot access the file 'C:\inetpub\wwwroot\Citrix\web.config' because it is being used by another process."...