UBUNTU: SAUCE: LSM stacking: LSM: General stacking

UBUNTU: SAUCE: LSM stacking: LSM: General stacking

BugLink: http://bugs.launchpad.net/bugs/1763062
Leverage the infrastructure management of the security blobs
to allow stacking of security modules in all but the most
extreme case. Security modules are informed of the location
of their data within the blobs at module initialization.

Stacking is optional. If stacking is not configured the old
limit of one "major" security module applies. If stacking is
configured TOMOYO can be configured with an of the other
modules. SELinux, Smack and AppArmor use (or in the AppArmor
case, threaten to use) secids, which are not (yet) shareable.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>