Add new filter 'ShelveAggregateAffinityFilter'

Add a new scheduler filter to schedule a shelved instance on the compute node
from the same hostaggregate group in case you have configured multiple
host aggregate groups with same metadata properties.

Use Cases:
When utilizing the 'improve-unshelve-performance' function[1] and
'shelved_offload_disk' is false, the suggested scheduling filter improves the
performance of unshelving an instance by scheduling the instance to the compute
node that have access to the instance files 'cache' in case of multiple host
aggregate groups sharing same metadata properties (image properties/instance
type etc).

[1] https://blueprints.launchpad.net/nova/+spec/improve-unshelve-performance