Prometheus metric names, types and units could be cleaner and more consistent

[ximon18]

Just some observations, there are probably more:

• rotonda_task_total_poll_count_total - contains the term total twice and also count.
• rotonda_rib_merge_update_announce_duration_microseconds_count - why does this count not end in _total (the metric type) while the one above does, do they have a different rotonda/rtrtr MetricUnit ?