Improve test portability

We have to ensure that the attempted connection to the MySQL server
fails, and do that by passing an unknown host instead of falling back
to localhost.

Author: cmb69

ext/mysqli/tests/mysqli_incomplete_initialization.phpt

@@ -8,7 +8,7 @@ require_once('skipif.inc');
 <?php
 
 $mysqli = new mysqli();
-@$mysqli->__construct(null);
+@$mysqli->__construct('doesnotexist');
 $mysqli->close();
 
 ?>