Move resource allocation ratios from scheduler to resource tracker

The memory and CPU allocation ratios are currently controlled on a global basis or per-aggregate, with the global configuration settings determined in the core_filter and ram_filter filter modules in the scheduler, and the per-aggregate allocation ratio overrides are stored in the aggregates table in the database, with the core_filter scheduler filter performing repeated lookups to the aggregates table to determine the allocation ratio to use when host aggregates are in use in the deployment.

Allocation ratios are NOT scheduler policy, and should not be either defined nor queried in the schedule at all. Allocation ratios are simply a way for a compute node to advertise that it has the ability to service more resources than it physically has available: an overcommit ratio. Therefore, not only does the total advertised amount of resources on a compute node NOT need to be recalculated on each run of the scheduler to find a compute node for an instance, but the resource tracker is the most appropriate place to set the available resource amounts.