graphite_metric_list_to_kairosdb_list in graphite.py wants uniform tags?

The comment, as written, says:

```
    Use this for entering a large set of metrics that have the same set of tags (e.g. same retentions, etc.)
```

I don't think this needs to be uniform, but if it does, do something like yielding multiple lists instead of returning a single list, bucketed by tags.
