Separate calculation of the CPU Utilization from Autoscaler Ticktock

[juliababkina]

Currently, cpu utilization calculation for plot in UI is tightly coupled with autoscaler ticktock https://github.com/pivotal/skenario/blob/master/sim/pkg/model/autoscaler_ticktock.go#L103. This logic should be separated and happens as another tick to have smoother line of the cpu utilization on the plot.
The cpu utilization tick should happens frequenter than 15 sec (default resync period), 2 seconds seems like a good period for calculation of the cpu utilization.