disk allocation ratio should move to resource tracker

[Eric Xie]

1. version:
nova 12.0.0 Liberty

2. As mentioned in https://blueprints.launchpad.net/nova/+spec/allocation-ratio-to-resource-tracker,
cpu/mem allocation ratio have already been moved to resource tracker.
And disk allocation ratio MUST be moved as same.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/245619

[Sylvain Bauza (sylvain-bauza)]

I actually opened a blueprint for that feature request. Since it's a scheduler-related effort, it is part of our Nova Priorities so it's not impacted by the non-priority Feature Freeze for Mitaka.

[Sylvain Bauza (sylvain-bauza)]

https://blueprints.launchpad.net/nova/+spec/disk-allocation-ratio-to-rt