Restore pipeline output variable for Agent OS name (Azure#16832)

Co-authored-by: Ben Broderick Phillips <[email protected]>

Author: azure-sdk

eng/common/pipelines/templates/steps/verify-agent-os.yml

@@ -13,4 +13,4 @@ steps:
       workingDirectory: $(System.DefaultWorkingDirectory)
       filePath: ${{ parameters.ScriptDirectory }}/Verify-AgentOS.ps1
       arguments: >
-        -AgentImage ${{ parameters.AgentImage }}
+        -AgentImage "${{ parameters.AgentImage }}"

eng/common/scripts/Verify-AgentOS.ps1

@@ -8,6 +8,14 @@ function Throw-InvalidOperatingSystem {
     throw "Invalid operating system detected. Operating system was: $([System.Runtime.InteropServices.RuntimeInformation]::OSDescription), expected image was: $AgentImage"
 }
 
-if ($AgentImage -match "windows|win|MMS2019" -and !$IsWindows) { Throw-InvalidOperatingSystem }
-if ($AgentImage -match "ubuntu" -and !$IsLinux) { Throw-InvalidOperatingSystem }
-if ($AgentImage -match "macos" -and !$IsMacOs) { Throw-InvalidOperatingSystem }
+if ($IsWindows -and $AgentImage -match "windows|win|MMS2019") {
+    $osName = "Windows"
+} elseif ($IsLinux -and $AgentImage -match "ubuntu") {
+    $osName = "Linux"
+} elseif ($IsMacOs -and $AgentImage -match "macos") {
+    $osName = "macOS"
+} else {
+    Throw-InvalidOperatingSystem
+}
+
+Write-Host "##vso[task.setvariable variable=OSName]$osName"