title: grafana prometheus use legend from other series
body: <p>have the following series and want use <code>host[host]</code> for legend instead of <code>instance</code>. can anyone help?</p>
  
  <p>first one:</p>
  
  <ul>
  <li><code>node_load1{instance=~"$node"}</code></li>
  <li><code>node_load1{instance="10.42.220.165:9100",job="HostsMetrics"}</code></li>
  </ul>
  
  <p>and the second one:</p>
  
  <ul>
  <li><code>host{instance=~"$node"}</code></li>
  <li><code>host{host="srv02.example.com",instance="10.42.220.165:9100",job="HostsMetrics",node="Prometheus-node-exporter-2"}</code></li>
  </ul>