Sync eng/common directory with azure-sdk-tools for PR 1953 (Azure#15413)

* Add random elements to default base name

* Fix principal

* tab

Co-authored-by: JoshLove-msft <54595583+JoshLove-msft@users.noreply.github.com>

eng/common/TestResources/New-TestResources.ps1

@@ -289,7 +289,8 @@ try {
                 $AzureTestPrincipal
             } else {
                 Log "TestApplicationId was not specified; creating a new service principal in subscription '$SubscriptionId'"
-                $global:AzureTestPrincipal = New-AzADServicePrincipal -Role Owner -Scope "/subscriptions/$SubscriptionId" -DisplayName "test-resources-$($baseName).microsoft.com"
+                $suffix = (New-Guid).ToString('n').Substring(0, 4)
+                $global:AzureTestPrincipal = New-AzADServicePrincipal -Role Owner -Scope "/subscriptions/$SubscriptionId" -DisplayName "test-resources-$($baseName)$suffix.microsoft.com"
                 $global:AzureTestSubscription = $SubscriptionId
 
                 Log "Created service principal '$($AzureTestPrincipal.ApplicationId)'"