Fix cgroup_regression_test.sh script issue

Testcase cgroup sometimes fail although there is no bug found.
Initialize the exit status to fix it.
Using "rmdir cgroup/" to clean up test_dir sometimes failed because
there may be subdir not removed in cgroup/.
Using "rmdir -p cgroup/*" instead.

Signed-off-by: Shuang Qiu <shuang.qiu@oracle.com>
Acked-by: Cyril Hrubis <chrubis@suse.cz>
Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>