.NET Core 2+ Naming and Versioning

New file name structure for the runtime and the CLI
per: https://github.com/dotnet/designs/issues/2

The renaming of assets, therefore the dotnet installation scripts must change to accommodate.

Trivial:
"Write-Host" should be "Write-Output"

scripts/dev-dotnet.ps1

@@ -15,7 +15,7 @@ try {
     if (Test-Path $stage2) {
         $env:PATH="$stage2;$env:PATH"
     } else {
-        Write-Host "You don't have a dev build in the 'artifacts\$rid\stage2' folder!"
+        Write-Output "You don't have a dev build in the 'artifacts\$rid\stage2' folder!"
     }
 
     dotnet @args