Download the stage0 dotnet tools from the beta feed for windows.

Set the correct channel so that the stage0 binaries are downloaded
correctly.

** This commit cannot be directly merged from the release branch to the
master branch **

scripts/publish/publish.ps1

@@ -7,6 +7,8 @@ param(
     [Parameter(Mandatory=$true)][string]$file
 )
 
+. "$PSScriptRoot\..\common\_common.ps1"
+
 function CheckRequiredVariables 
 {
     if([string]::IsNullOrEmpty($env:DOTNET_CLI_VERSION))