Persist per-machine welcome location

scripts/Set-SguWelcomeWallpaper.ps1

@@ -305,6 +305,14 @@ if (-not (Test-Path -LiteralPath $BaseImagePath -PathType Leaf)) {
 
 $userName = [Environment]::UserName
 $metadata = $null
+$machineLocation = [Environment]::GetEnvironmentVariable('SGU_WELCOME_LOCATION', 'Machine')
+$machineOrganizationalUnit = [Environment]::GetEnvironmentVariable(
+    'SGU_WELCOME_ORGANIZATIONAL_UNIT',
+    'Machine')
+if (-not $machineLocation) { $machineLocation = $env:SGU_WELCOME_LOCATION }
+if (-not $machineOrganizationalUnit) {
+    $machineOrganizationalUnit = $env:SGU_WELCOME_ORGANIZATIONAL_UNIT
+}
 if (-not $SkipDirectoryLookup) {
     try {
         $metadata = Get-DirectoryWelcomeMetadata -UserName $userName -MachineName $ComputerName
@@ -320,8 +328,8 @@ if (-not $PSBoundParameters.ContainsKey('DisplayName')) {
 if (-not $DisplayName) {
     $DisplayName = $userName
 }
-if (-not $PSBoundParameters.ContainsKey('Location') -and $metadata) {
-    $Location = $metadata.Location
+if (-not $PSBoundParameters.ContainsKey('Location')) {
+    $Location = if ($machineLocation) { $machineLocation } elseif ($metadata) { $metadata.Location } else { $null }
 }
 $genderWasProvided = $PSBoundParameters.ContainsKey('Gender')
 if (-not $genderWasProvided -and $metadata -and $metadata.Gender -in @('Male', 'Female')) {
@@ -330,8 +338,16 @@ if (-not $genderWasProvided -and $metadata -and $metadata.Gender -in @('Male', '
     $Gender = $metadata.Gender
 }
 $welcomeHeading = Get-WelcomeHeading -Gender $Gender
-if (-not $PSBoundParameters.ContainsKey('OrganizationalUnit') -and $metadata) {
-    $OrganizationalUnit = $metadata.OrganizationalUnit
+if (-not $PSBoundParameters.ContainsKey('OrganizationalUnit')) {
+    $OrganizationalUnit = if ($machineOrganizationalUnit) {
+        $machineOrganizationalUnit
+    }
+    elseif ($metadata) {
+        $metadata.OrganizationalUnit
+    }
+    else {
+        $null
+    }
 }
 $locationText = Get-WelcomeLocationText -Room $Location -OuName $OrganizationalUnit -Gender $Gender