apparmor: Allow bind-mounts and {r}shared/{r}private

apparmor: Allow bind-mounts and {r}shared/{r}private

Bind-mounts aren't harmful in containers, so long as they're not used to
bypass MAC policies.

This change allows bind-mounting of any path which isn't a dangerous
filesystem that's otherwise blocked by apparmor.

This also allows switching paths {r}shared or {r}private.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>