Record counters as CUMULATIVE metrics

[n-oden]

This addresses #18

While using |align delta_gauge() in MQL is potentially a workaround, it suffers from the drawback of producing huge negative deltas when the counter resets, and the current behavior is unhappily surprising to first-time users who would reasonably assume that IncrCounter() would produce a CUMULATIVE metric.

Signed-off-by: Nathan J. Mehl n@oden.io

[n-oden]

FWIW: I believe that this approach avoids the difficulties encountered in #19 -- the stackdriver API for CUMULATIVE metrics is extremely fussy about start/end times, and there's really no getting around needing to keep track of your own start time.

[n-oden]

@tam7t thoughts? :) We've worked around this locally by copy-pasting a patched stackdriver.go into our codebase (and can confirm that it works as expected) so there's no hurry precisely but I'd love to know if you consider this acceptable.

[tam7t]

@n-oden thanks for the contribution! this seems reasonable I just want to test it out manually some and see the behavior if the metrics are already defined in stackdriver as a gauge. Depending on that behavior I may want to provide some docs on deleting metrics or some migration path.

[n-oden]

@tam7t thanks! I'll revert out the go.mod changes that seem to have broken some of the tests. (That was a result of my reflexively running go mod tidy in my local workspace -- I don't think the PR depends on any of it.)

[n-oden]

@tam7t oh, and btw I can tell you what the behavior will be with existing gauge metrics: an error from the GCM driver that says it can't update the metric due to a metric_kind mismatch. :(

Happy to write up a note explaining things -- should it go in the README or elsewhere?

[n-oden]

@tam7t happy new year! I've updated the README to give people a heads up about the changed behavior.

[tam7t]

Thank you for adding the instructions! Merging now, it may take me a bit to cut a new release but it should be fetchable from HEAD now!

[n-oden]

Hey @tam7t following up here -- any chance that we could get an 0.6.0 release cut? In addition to wanting the fixes in this PR, the go-metrics package itself has moved from github.com/armon/ to github.com/hashicorp/, so v0.5.0 now presents some dependency issues.