Aggregates

[fujiwara]

Add aggregate feature.

aggregates works as below.

1. Fetch hosts information from Mackerel API.
   • Filtered service and role.
2. For each hosts, fetch specified host metrics to calculates these metrics by functions.
3. Post theses aggregated metrics as Mackerel service metrics.
4. Iterates these processes each 60 sec.

It is useful for monitoring the long span aggregated host metrics.