Goal: 

• As a deployer, I Want collect worker utilization statistics from futurists ThreadPoolExecutors, so that I can easily detect when the deployment needs performance tuning, i.e. if the pool is underutilized then the size can be decreased, if the pool is close to be fully utilized then the size needs to be increased.

Acceptance Criteria:

• The futurist lib's ExecutorStatistics class contains utilization statistics aggregated across the workers in the pool. The utilization is calculated as a sum of time executed  across the workers divided by N times wall clock time elapsed, where N is the number of workers.
• The in progress nova eventlet-removal series logs the new statistics as part of the semi periodic stats logging.