tools/virtio/ringtest: fix run-on-all.sh to work without /dev/cpu

#use last CPU for host. Why not the first?

#many devices tend to use cpu0 by default so

#it tends to be busier

HOST_AFFINITY=$(cd /dev/cpu; ls|grep -v '[a-z]'|sort -n|tail -1)

HOST_AFFINITY=$(lscpu -p=cpu | tail -1)

#run command on all cpus

for cpu in $(cd /dev/cpu; ls|grep -v '[a-z]'|sort -n);

for cpu in $(seq 0 $HOST_AFFINITY)

do

	#Don't run guest and host on same CPU

	#It actually works ok if using signalling