LU-549 llite: Improve statfs performance if selinux is disabled

LU-549 llite: Improve statfs performance if selinux is disabled

Don't disable all security xattrs when selinux is disabled just
disable security.selinux. Disabling all security xattrs was
overreaching and causing issues at a customer site.

This patch is built ontop of the original patch:
commit 7cc542fd4c26ccb117ceb13a47ac8ced3107b9b3.

Signed-off-by: Keith Mannthey <keith@whamcloud.com>
Change-Id: I73482d2ff1f166a48dceb3737df0e9e1b187dc85
Reviewed-on: http://review.whamcloud.com/2955
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>