UBUNTU: SAUCE: LSM stacking: LSM: manage credential security blobs

UBUNTU: SAUCE: LSM stacking: LSM: manage credential security blobs

Move the management of credential security blobs from the
individual security modules to the security infrastructure.
The security modules using credential blobs have been updated
accordingly. Modules are required to identify the space they
require at module initialization. In some cases a module no
longer needs to supply blob management hook, in which case
the hook has been removed.

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>