Merge branch 'montcalm-kwollect' into 'master'

[toulouse][montcalm] set same values for prometheus' metrics as other clusters

See merge request grid5000/reference-repository!629

data/grid5000/sites/toulouse/clusters/montcalm/montcalm.json

@@ -842,7 +842,8 @@
     {
       "description": "Default subset of metrics from Prometheus Node Exporter",
       "name": "prom_default_metrics",
-      "period": 15000,
+      "optional_period": 15000,
+      "period": 0,
       "source": {
         "id": [
           "node_boot_time_seconds",

input/grid5000/sites/toulouse/clusters/montcalm/montcalm_metrics.yaml

@@ -582,7 +582,8 @@ metrics:
 
   - name: prom_default_metrics
     description: Default subset of metrics from Prometheus Node Exporter
-    period: 15000
+    period: 0
+    optional_period: 15000
     source:
       protocol: prometheus
       port: 9100