Unify runtime usage counters name

[pwalski]

Unify runtime counter names so all of them will use underscore separator

"golem.usage.duration_sec",
"golem.usage.gpu_sec"

(update counter names in runtime main.rs, offer template, gamerhash-facade automatic descriptor, golem lib code & tests)

[nieznanysprawiciel]

We are migrating in opposite direction

[pwalski]

that was fast