Use pre-release Packer for Windows on Hyper-V

Fix for hashicorp/packer#7278

AppVeyorBYOC-Common.ps1

@@ -238,8 +238,8 @@ function ValidateDependencies ($cloudType) {
     }
 }
 
-function GetPackerPath {
-    $packerVersion = "1.4.3"
+function GetPackerPath ([switch]$prerelease) {
+    $packerVersion = if ($prerelease) {"1.4.4"} else {"1.4.3"}
     Write-host "`nChecking if Hashicorp Packer version $packerVersion is installed..."  -ForegroundColor Cyan
     if ((Get-Command packer -ErrorAction Ignore) -and (packer --version) -eq $packerVersion) {
         Write-Host "Packer version $packerVersion found" -ForegroundColor DarkGray
@@ -252,7 +252,8 @@ function GetPackerPath {
         $currentSecurityProtocol = [System.Net.ServicePointManager]::SecurityProtocol
         $zipFile = if ($isLinux) {"packer_$($packerVersion)_linux_amd64.zip"} elseif ($isMacOS) {"packer_$($packerVersion)_darwin_amd64.zip"} else {"packer_$($packerVersion)_windows_amd64.zip"} 
         [System.Net.ServicePointManager]::SecurityProtocol = "Tls12"
-        (New-Object Net.WebClient).DownloadFile("https://releases.hashicorp.com/packer/$packerVersion/$zipFile", $zipPath)
+        $URL = if ($prerelease) {"https://github.com/appveyor/build-images/releases/download/packer-1.4.4/packer_windows_amd64.zip"} else {"https://releases.hashicorp.com/packer/$packerVersion/$zipFile"}
+        (New-Object Net.WebClient).DownloadFile($URL, $zipPath)
         [System.Net.ServicePointManager]::SecurityProtocol = $currentSecurityProtocol
         Expand-Archive -LiteralPath $zipPath -DestinationPath $packerFolder
         Remove-Item $zipPath -force -ErrorAction Ignore

Connect-AppVeyorToHyperV.ps1

@@ -199,7 +199,7 @@ d-i passwd/user-default-groups appveyor sudo
 
         #Run Packer to create an VHD
         if (-not $VhdPath) {
-            $packerPath = GetPackerPath
+            $packerPath = if ($imageOs -eq "Windows") {$(GetPackerPath -prerelease)} else {$(GetPackerPath)}
             $packerManifest = "$(CreateTempFolder)/packer-manifest.json"
             Write-host "`nRunning Packer to create a basic build VM VHD..." -ForegroundColor Cyan
             Write-Warning "Add '-VhdPath' parameter with if you want to to skip Packer build and and reuse existing VHD."