staging: lustre: llite: basic support of SELinux in CLIO

Bring the ability to properly initiate security context
on SELinux-enabled client and store it on server side via
extended attribute.

Security context initialization is not atomic, but that would
require a wire protocol change to send security label in the
creation request.

Filter out security.selinux from xattr cache as it is
already cached in system slab.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5560
Reviewed-on: http://review.whamcloud.com/11648


Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>