TT#129100 Switch grafana data sources from InfluxDB to Prometheus

We have removed InfluxDB support, so datasources for that monitoring
backend will not be present. Add the Prometheus ones which were
previously missing.

Change-Id: I5b6cc5f78571c45e282437faa615d2400f0c10a6

templates/911_service-grafana.yaml.tt2

@@ -19,7 +19,6 @@ command:
   sqlite3 /var/lib/grafana/grafana.db "select name from data_source":
     exit-status: 0
     stdout:
-    - "/^ngcp$/"
-    - "/^telegraf$/"
+    - "/^Prometheus$/"
     stderr: []
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