Correcting test for Config.class.php 

The constant used to load config file i.e **CONFIG_FILE** in (vendour_config.php) was **config.inc.php** (for creating **$GLOBALS['PMA_Config']** object ) while it did not exist in code base (as **config.sample.inc.php** exist in code ), thus creating a testcase similar to one for **PMA_ConfigTest::object**

This was also causing **PMA_ConfigTest::testCheckPermissions()** to fail. 
The parameter passed to the constructor of PMA_Config i.e CONFIG_FILE has been replaced with "**config.sample.inc.php**", so that assertions can be applied to object with configurations loaded from file
 
Signed-off-by: A V Minhaz <minhazav@gmail.com>