apparmor: use /{,**} instead of /**

apparmor: use /{,**} instead of /**

It turned out, that old (and incorrect) rule:
mount options=(rw,make-slave) -> **,

is NOT equivalent to:
mount options=(rw,make-slave) -> /**,

Let's use:
mount options=(rw,make-slave) -> /{,**},

Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>