Add a simple test to verify that an empty v1 cpuset will force its tasks to be moved to an ancestor node. It is based on the test case documented in commit 76bb5ab8f6e3 ("cpuset: break kernfs active protection in cpuset_write_resmask()"). Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org>