Use pre-existing metric for log messages

[bboreham]

Someone copy-pasted this code with the result that it sometimes worked and sometimes didn't.

I think this way is better.

[coveralls]

Coverage decreased (-4.3%) to 85.714% when pulling 891381c on reuse-log-metric into 0599d76 on master.

[bboreham]

The test that is failing requires the old behaviour.

IDK; I think double-counting if you manage to register the same hook twice is better than unregistering something that someone else might have been using.

[marccarre]

@bboreham, what do you now think about keeping the logic to unregister, but having namespacing, like you suggested initially in cortexproject/cortex/issues/666? That way, no double counting, and less chance of accidentally unregistering something else? Maybe promrus_log_messages_total?

[bboreham]

@marccarre in the case where I hit this, the other person was deliberately trying to match the name used here, to avoid disruption. But they didn't anticipate both libraries being in the same program.

[bboreham]

Very old, closing.