Update haproxy events

- add haproxy agent name in the title
- add backend in the tags
- align with metrics tags
![screen shot 2014-05-23 at 5 18 02 pm](https://cloud.githubusercontent.com/assets/1532259/3071993/ed7b0d48-e2bf-11e3-9568-f23d2f7f1e2b.png)