apparmor: fix profile lookup for unconfined

BugLink: http://bugs.launchpad.net/bugs/978038

also affects apparmor portion of
BugLink: http://bugs.launchpad.net/bugs/987371



The unconfined profile is not stored in the regular profile list, but
change_profile and exec transitions may want access to it when setting
up specialized transitions like switch to the unconfined profile of a
new policy namespace.

Signed-off-by: John Johansen <john.johansen@canonical.com>