Update grafana example for diskio

Taking into account time_since_update in a similar manner to networks

conf/glances-grafana.json

@@ -1243,7 +1243,7 @@
           "measurement": "localhost.diskio",
           "orderByTime": "ASC",
           "policy": "default",
-          "query": "SELECT mean(\"$disk.read_bytes\") FROM \"localhost.diskio\" WHERE $timeFilter GROUP BY time($__interval) fill(none)",
+          "query": "SELECT mean(\"$disk.read_bytes\")/mean(\"$disk.time_since_update\") FROM \"localhost.diskio\" WHERE $timeFilter GROUP BY time($__interval) fill(none)",
           "rawQuery": true,
           "refId": "A",
           "resultFormat": "time_series",
@@ -1286,7 +1286,7 @@
           "measurement": "localhost.diskio",
           "orderByTime": "ASC",
           "policy": "default",
-          "query": "SELECT mean(\"$disk.write_bytes\") FROM \"localhost.diskio\" WHERE $timeFilter GROUP BY time($__interval) fill(none)",
+          "query": "SELECT mean(\"$disk.write_bytes\")/mean(\"$disk.time_since_update\") FROM \"localhost.diskio\" WHERE $timeFilter GROUP BY time($__interval) fill(none)",
           "rawQuery": true,
           "refId": "B",
           "resultFormat": "time_series",
@@ -3183,4 +3183,4 @@
   "title": "Glances",
   "uid": "000000002",
   "version": 10
-}
\ No newline at end of file
+}