Move allocation ratios to resource tracker

Proposal to move the allocation ratio definitions out of the scheduler
filters and into the resource tracker, and move the calculation of
available resources (with overcommit ratio) into the host manager in the
scheduler instead of in the filters themselves

Change-Id: Ic3c3029cf48177e050da2b4a9bb49a21906d82db
Blueprint: allocation-ratio-to-resource-tracker
Merge "Move allocation ratios to resource tracker"