因为要绘制曲线，所以不希望promsql返回空置。​

关键：or vector(0)

count(instance:node_cpu_utilisation:rate5m{cluster='prod-hangzhou-k8s06',instance!~'cn-hangzhou'}>0.15)or vector(0)/count(instance:node_cpu_utilisation:rate5m{cluster='prod-hangzhou-k8s06',instance!~'cn-hangzhou'})*100