Clarify effect of cpu_allocation_ratio setting

Clarify that the cpu_allocation_ratio only takes effect
internally in the scheduler. That changes to this value
are not reflected in the API, CLI, and dashboard is a
common source of confusion.

Change-Id: I48af4e47675f9476cd93253386b7cd45baefcb67
Merge "Clarify effect of cpu_allocation_ratio setting"