adds check_metrics for two DRBD checks

[gurubert]

both collect the metrics in KiB/s

The resulting graphs were not very pretty.

[mo-ki]

Hi Robert! I think we should rather fix the plugin (to produce nice metrics) and then add the translation in the other direction to provide some backwards compatibility.

[logan-connolly]

Hi @gurubert, thank you for bringing this to our attention! I investigated this topic and found the following things:

1. one of my colleagues took care of adding translations to drbd net and drbd disk back in August so a change to the translations isn't needed at the moment.
2. the scaling for both these metrics didn't match kb as the unit of measure. So in this change we are now using the appropriate render functions for the scaled metrics.

FYI: we also went ahead and migrated the drbd plugins from legacy to v2. This explains the changed code and file paths.

Closing this since the translations were indirectly picked up in August. The graphs should be more clear in the upcoming 2.4 release. If we missed the mark, feel free to reach out again. Thanks again for your contribution! :)