This patch updates how cinder calculates it's free capacity.
The new calculations are based off of the queens cinder specs
that describes each of the capacity factors here:
https://specs.openstack.org/openstack/cinder-specs/specs/queens/provisioning-improvements.html
This patch updates the capacity filter to use the new capacity factors
calculations, which is also used by the capacity weigher.
The new calculate_capacity_factors describes each of the factors and
returns a dictionary of each of the factors as calculated.
Change-Id: Ic1b5737281e542d2782089a369e4b7941fc3d921