core: You can not put the cached result of use_smack fct, as we are not sure...

core: You can not put the cached result of use_smack fct, as we are not sure the "/sys" is mounted. So we should mount "sys" before "/proc"

https://bugs.freedesktop.org/show_bug.cgi?id=77646
(cherry picked from commit d1d8e5d4)