LU-1818 quota: en/disable quota enforcement via conf_param

LU-1818 quota: en/disable quota enforcement via conf_param

In the new quota architecture, quota is enabled/disabled
per-filesystem, by 'lctl conf_param':

lctl conf_param $FSNAME.quota.$POOLNAME=$VAL

$FSNAME  : filesystem name;
$POOLNAME: 'mdt' (for meta pool) or 'ost' (for data pool);
$VAL     : 'none' - disable both,
           'u'    - enable user quota,
           'g'    - enable group quota,
           'ug'   - enable both;

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I89ef9fc1a067981cf7caac29c8311b75054c91fe
Reviewed-on: http://review.whamcloud.com/3850
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>