Smack: Cgroup filesystem access

Smack: Cgroup filesystem access

The cgroup filesystems are not mounted using conventional
mechanisms. This prevents the use of mount options to
set Smack attributes. This patch makes the behavior
of cgroup filesystems compatable with the way systemd
uses them.

Change-Id: I1e0429f133db9e14117dc754d682dec08221354c
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Stephane Desneux <stephane.desneux@open.eurogiciel.org>