Adds info on pairing host aggregates and custom flavors

AggregateInstanceExtraSpecsFilter, AggregateCoreFilter, and
AggregateRamFilter allow for customizing high compute and
low compute workloads into aggregates with different resource
allocation ratios

Change-Id: I67bb039bf2050cc7260775247693b651140360d9
Merge "Adds info on pairing host aggregates and custom flavors"