consistent metrics mapping to influx miner_system and miner_gpu fields

[rodneymo]

Metrics can have different meanings across different miners. Harmonizing them into a common influx schema has the benefit of allowing dashboards to be reused.

I have captured the mapping for sgminer and claymore here. @wishbone1138 , could you take a look?

Specific to claymore I don't understand the different between rejected and incorrect. I have never seen a rejected share, only incorrect shares (due to excessive GPU OC). Also claymore doesn't seem to capture stale shares, which sgminer does