Enable persistent connections for IBMi

'db' => array(
        'driver' => 'IbmDb2',
        'database' => '*LOCAL',
        'username' => 'USER',
        'password' => 'PASSWORD',
        'persistent' => true,
        'driver_options' => array(
            'i5_naming' => DB2_I5_NAMING_ON,
            'i5_libl' => 'SOMELIB QGPL'
        ),
        'platform_options' => array(
            'quote_identifiers' => false
        )
    ),

'persistent' accepts true/false, or can be left out

Change-Id: I8b42f83e7be794286fc5b23e8dc195bb22b23b66