Alert on any collectd metric via bosh manifest

[cnelson]

In order to quickly and reliably alert on any metric generated by collectd as an SRE I want to be able to add additional collectd metrics to riemann by only editing the bosh manifest.

Acceptance Criteria

• Any collectd generated metric can be alerted on by updating the bosh manifest and without writing clojure
• Tests exist for collectd alerts and are run before each monitoring deployment^🌮

🌮 - This should be covered by our DoD but we have NO tests for riemann alerts right now so figuring out the right way to write riemann tests and integrating them into our deployment pipeline is going to take a non-trivial amount of work the first time we do it so I thought that effort should be highlighted with an AC.

cc: @jmcarp @sharms #509

Implementation Sketch
See this slack thread