torture: Add --no-affinity parameter to kvm.sh

In performance tests, it can be counter-productive to spread torture-test
guest OSes across sockets.  Plus the experimenter might have ideas about
what CPUs individual guest OSes are to run on.  This commit therefore
adds a --no-affinity parameter to kvm.sh to prevent it from running
taskset on its guest OSes.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>