move mysqli connection test to new namespace

tests/Doctrine/Tests/DBAL/Functional/Mysqli/ConnectionTest.php → tests/Doctrine/Tests/DBAL/Functional/Driver/Mysqli/ConnectionTest.php

 <?php
-namespace Doctrine\Tests\DBAL\Functional\Mysqli;
+namespace Doctrine\Tests\DBAL\Functional\Driver\Mysqli;
 
 class ConnectionTest extends \Doctrine\Tests\DbalFunctionalTestCase
 {