Fix double dots .. in metric keys

[mkcp]

In the process of building up the dot-delimited metric keys for http paths, consul.http.GET.v1.token we sometimes emit keys with two contiguous dots, e.g. consul.http.GET.v1.token..count. We suspect that these keys are being emitted as consul.http.GET.v1.token._.count with the empty string being replaced with an underscore, but that underscore gets trimmed by dogstatsd.

We can narrow this down by running a local receiver for the dogstatsd protocol and inspecting the wire traffic to see if it's a problem within Consul, or a quirk of Grafana and/or the dogstatsd protocol.

Once we localize the issue, we probably want to figure out a way to fix it and deprecate the old double-dot metrics.

Slack thread identifying the issue https://hashicorp.slack.com/archives/C045NJD17/p1595263451020200

[mkcp]

A bit of googling confirmed that - and _ are trimmed by the dogstatd. I haven't isolated exactly where this occurs, but that's enough information that we can try to build a workaround.

[mkcp]

Resolved by #8271

[mkcp]

Resolved in 1.9