Tests: fix PreserveAsyncOrder_SetConnectionMultiplexerProperty

This was correctly blowing up as we don't run that test server...ignore that with a valid server and test what we actually wanted to test.

StackExchange.Redis.Tests/Issues/Issue791.cs

@@ -32,7 +32,7 @@ public void DefaultValue_IsTrue()
         [Fact]
         public void PreserveAsyncOrder_SetConnectionMultiplexerProperty()
         {
-            var multiplexer = ConnectionMultiplexer.Connect(TestConfig.Current.MasterServer + ":6500,preserveAsyncOrder=false");
+            var multiplexer = ConnectionMultiplexer.Connect(TestConfig.Current.MasterServer + ":" + TestConfig.Current.MasterPort + ",preserveAsyncOrder=false");
             Assert.False(multiplexer.PreserveAsyncOrder);
         }
     }