to #26424323

For container only cases, since guest cputime is always 0, we don't
calculate it and return 0 directly before.

Howerver, when running vm inside a cgroup, we expect the cgroup to
maintain guest cputime correctly.
Tested-by: NYihao Wu <wuyihao@linux.alibaba.com>
Signed-off-by: NShanpei Chen <shanpeic@linux.alibaba.com>
Reviewed-by: NShanpei Chen <shanpeic@linux.alibaba.com>
Signed-off-by: NYihao Wu <wuyihao@linux.alibaba.com>