Add support for qos_specs feature to solidfire driver

We've added a new qos_specs object to Cinder that allows creation and management of qos settings separate from volume-types. Now instead of embedding the qos info in the extra-specs of the volume-type we associate the desired qos-spec to a volume-type.

The capability to check for this and use it needs to be added to the SolidFire driver. The default method of the reading extra-specs will still work and be a valid mode of setting QoS, however if the association is present it will over-ride any settings in the extra-specs.