cgroup/cpuset: Move housekeeping_update()/rebuild_sched_domains() together

cgroup/cpuset: Move housekeeping_update()/rebuild_sched_domains() together

With the latest changes in sched/isolation.c, rebuild_sched_domains*()
requires the HK_TYPE_DOMAIN housekeeping cpumask to be properly
updated first, if needed, before the sched domains can be
rebuilt. So the two naturally fit together. Do that by creating a new
update_hk_sched_domains() helper to house both actions.

The name of the isolated_cpus_updating flag to control the
call to housekeeping_update() is now outdated. So change it to
update_housekeeping to better reflect its purpose. Also move the call
to update_hk_sched_domains() to the end of cpuset and hotplug operations
before releasing the cpuset_mutex.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>