Message definition (ReleaseNotes/Juno )
* Extensible Resource Tracking. The set of resources tracked by nova is hard coded, this change makes that extensible, which will allow plug-ins to track new types of resources for scheduling. [https://blueprints.launchpad.net/nova/+spec/extensible-resource-tracking launchpad] [http://specs.openstack.org/openstack/nova-specs/specs/juno/extensible-resource-tracking specification]
* Extensible Resource Tracking. The set of resources tracked by nova is hard coded, this change makes that extensible, which will allow plug-ins to track new types of resources for scheduling. [https://blueprints.launchpad.net/nova/+spec/extensible-resource-tracking launchpad] [http://specs.openstack.org/openstack/nova-specs/specs/juno/extensible-resource-tracking specification]
* Allow a host to be evacuated, but with the scheduler selecting destination hosts for the instances moved. [https://blueprints.launchpad.net/nova/+spec/find-host-and-evacuate-instance launchpad] [http://specs.openstack.org/openstack/nova-specs/specs/juno/find-host-and-evacuate-instance specification]
* Add support for host aggregates to scheduler filters. launchpad: [https://blueprints.launchpad.net/nova/+spec/per-aggregate-disk-allocation-ratio disk]; [https://blueprints.launchpad.net/nova/+spec/per-aggregate-max-instances-per-host instances]; and [https://blueprints.launchpad.net/nova/+spec/per-aggregate-max-io-ops-per-host IO ops] [http://specs.openstack.org/openstack/nova-specs/specs/juno/per-aggregate-filters specification] 
