[System] Fixes SmtpClientTest.Deliver_Async

mcs/class/System/Test/System.Net.Mail/SmtpClientTest.cs

@@ -404,6 +404,8 @@ namespace MonoTests.System.Net.Mail
 			Assert.AreEqual ("<[email protected]>", server.mail_from);
 			Assert.AreEqual ("<[email protected]>", server.rcpt_to);
 
+			task.Wait (10);
+
 			Assert.IsTrue (task.IsCompleted, "task");
 		}