workaround for locked PDBs causing delete on cleanup to fail

Author: gbiellem

src/ServiceControl.AcceptanceTests/AcceptanceTest.cs

@@ -215,7 +215,10 @@ static void Delete(string path)
                     Directory.SetAccessControl(path, directorySecurity);
                 }
 
-                Directory.Delete(path);
+                if (!Directory.GetFiles(path).Any())
+                {
+                    Directory.Delete(path);
+                }
             }
             finally
             {