Include an external health check

[mjallday]

Currently if whatever is feeding updates to the app goes down this will not be reflected. Consider integrating an external health check to augment and fix this.

[josegonzalez]

You may want to check for abnormalities in the data being aggregated. For example, graphite-pager will alert if there is No data for a check https://github.com/philipcristiano/graphite-pager/blob/master/graphitepager/worker.py#L99