cgroup/cpuset: Minor updates to test_cpuset_prs.sh

This patch makes the following minor updates to the cpuset partition
testing script test_cpuset_prs.sh.

 - Remove online_cpus function call as it will be called anyway on exit
   in cleanup.
 - Make the enabling of sched/verbose debugfs flag conditional on the
   "-v" verbose option and set DELAY_FACTOR to 2 in this case as cpuset
   partition operations are likely to be slowed down by enabling that.

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