Metrics: Calculation set to average always sums

[mwillbanks]

This commit is two part:

1. getActiveValueAttribute should always return the active attribute
   without any further calculation here. My guess is that this should also happen with sum but I was not going to modify it due to implications on the PR itself.

2. The query to create the average was incorrect and was taking the
   count value * the value which we are really looking for the average of
   the value.

[jbrooksuk]

Hmm, is this correct? The counter is used as a "how many times has this value been receieved in x time?" so surely we'd still need that, even for averages.

[jbrooksuk]

The query to create the average was incorrect and was taking the
count value * the value which we are really looking for the average of
the value.

No it wasn't? It was value * counter, then averaged that out.

[mwillbanks]

@jbrooksuk so while it looks like that was the case, then there are other issues. When I was pushing in values once per second, the value on the chart would increment, say an average of 12 would be quickly be 200+.

So in this case, you would sum the value and sum the counter and then take the division over a specific time period.

[jbrooksuk]

Do you need to change the threshold then?

[mwillbanks]

Aha, this looks to be the bug that is mentioned in: #1922