Grafana: show disk performance w_await by default

[innerr]

Now we have await which represents both read and write.
In the case of a few high latency read + a lot of low latency write, we will miss a lot infomation

[innerr]

https://www.robustperception.io/mapping-iostat-to-the-node-exporters-node_disk_-metrics

[innerr]

[innerr]

The picture above shows what we could miss:

• the await is low
• the w_await is low too
• but the r_wait is very high

If this happens, we can't learn it from Grafana for now

[innerr]

Actually grafana already collected the r_awaiit and w_await metrics, but w_await is not shown by default, we should display it by default