sensu alerts format

Hi,

I'm working on integration between kapacitor and Sensu and it seems I've triggered a bug in alerts format check.
I've seen in #240 that you check for output to match expected sensu format before submit the request to it. However since introduction of #1299 you add a handler id to the alert ID. And this does not match the regex:
```
[chronograf-v1-80112a77-e1eb-4c6c-a41b-81b3d96b3ca5:alert3] 2017/06/29 17:24:10 E! failed to send event to Sensu invalid name "load:nil" for sensu alert. Must match ^[\w\.-]+$
```
Is this a bug or a missunderstanding from me.

Thanks.

Start by tracing the Sensu integration's alert-format validation and the alert ID construction associated with handler IDs. Reproduce the reported `load:nil` rejection, then verify that the submitted alert name satisfies Sensu's stated format without breaking the handler ID behavior.

Written by the indexing model from the issue text.