Prometheus: move the name relabaling to metric_relabel_configs

Prometheus does not replace the metrics name when it also needs to
replace the __address__.

To overcome this, we can move the __name__ relabling to the
metric_relabel_configs section, which is perform after the
relabel_config part.

prometheus/prometheus.yml.template

@@ -40,6 +40,7 @@ scrape_configs:
       regex:  '(.*):\d+'
       target_label: instance
       replacement: '${1}'
+  metric_relabel_configs:
     - source_labels: [__name__]
       regex:  'node_disk_read_bytes_total'
       target_label: __name__