Metrics configuration can be inconsistent

[keith-turner]

The configuration for reporting metrics is currently pulled from the Fluo config file. This config file could be different for different processes running Fluo. For example Observers run by workers could easily have different configuration than Loaders running in a spark job. This could cause inconsistent metrics reporting for a Fluo application. One solution to this would be to push metrics config into zookeeper.

Reviewing #767 made me think about this issue. This config consistency issue predates the changes in #767.