test13: setup correctly

remove xxx/b;  chown xxx to $uid;  create xxx/b as $uid;  now xxx/b's
settings can be modified by $uid, and xxx/b starts out with full
memory limit.  So $uid can change the limit, and we can check whether
the new limit was set.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
add test of INvalid unprivileged cgroup setting

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>