libcontainer: setup cpuset cgroup by default

Currently if we don't use --cpuset, the cpuset cgroup is not
created, it's bad if we want to modify cpuset config subsequently,
change the behavior to make it right.

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
Ok, thanks. I'll take your commit and update it to ensure that the fs code is the same.