Compliancy the default metrics with Prometheus Naming Convention

[izonder]

Checking the default metrics with promtool complains about breaking compliancy with official Prometheus Naming Convention (https://prometheus.io/docs/practices/naming/), e.g.:

$ curl -s http://localhost:3000/metrics | promtool check metrics
nodejs_active_handles_total non-counter metrics should not have "_total" suffix
nodejs_active_requests_total non-counter metrics should not have "_total" suffix

[SimenB]

PR very much welcome fixing all metric names!

[izonder]

@SimenB please review the PR