kube-prometheus: Improve disk alert

Only trigger disk running full alerts when the disk capacity is over 85%
and use recording rule of the kubernetes-mixin to only consider real
physical filesystems.

jsonnet/kube-prometheus/alerts/node.libsonnet

@@ -7,11 +7,10 @@
           {
             alert: 'NodeDiskRunningFull',
             annotations: {
-              description: 'device {{$labels.device}} on node {{$labels.instance}} is running full within the next 24 hours (mounted at {{$labels.mountpoint}})',
-              summary: 'Node disk is running full within 24 hours',
+              message: 'Device {{ $labels.device }} of node-exporter {{ $labels.namespace }}/{{ $labels.pod }} is running full within the next 24 hours.',
             },
             expr: |||
-              predict_linear(node_filesystem_free{%(nodeExporterSelector)s,mountpoint!~"^/etc/(?:resolv.conf|hosts|hostname)$"}[6h], 3600 * 24) < 0 and on(instance) up{%(nodeExporterSelector)s}
+              (node:node_filesystem_usage: > 0.85) and (predict_linear(node:node_filesystem_avail:[6h], 3600 * 24) < 0)
             ||| % $._config,
             'for': '30m',
             labels: {
@@ -21,11 +20,10 @@
           {
             alert: 'NodeDiskRunningFull',
             annotations: {
-              description: 'device {{$labels.device}} on node {{$labels.instance}} is running full within the next 2 hours (mounted at {{$labels.mountpoint}})',
-              summary: 'Node disk is running full within 2 hours',
+              message: 'Device {{ $labels.device }} of node-exporter {{ $labels.namespace }}/{{ $labels.pod }} is running full within the next 2 hours.',
             },
             expr: |||
-              predict_linear(node_filesystem_free{%(nodeExporterSelector)s,mountpoint!~"^/etc/(?:resolv.conf|hosts|hostname)$"}[30m], 3600 * 2) < 0 and on(instance) up{%(nodeExporterSelector)s}
+              (node:node_filesystem_usage: > 0.85) and (predict_linear(node:node_filesystem_avail:[30m], 3600 * 2) < 0)
             ||| % $._config,
             'for': '10m',
             labels: {