rcutorture: Test RCU-tasks multiqueue callback queueing

This commit modifies the TASKS01 scenario to use four callback queues
and the TRACE01 scenario to use two queues, thus providing testing of
multiple queues by default.

Cc: Neeraj Upadhyay <neeraj.iitr10@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>