Enhancement request: QoS retype

[scaleoutsean]

With solidfire-san I can write a script to get the QoS option value for the volume, update QoS and the tag, but it requires an extra, DIY step.

Would it be too much trouble to add this? If a "generic" docker volume modify isn't possible, we could still consider .. -o from=<source_docker_volume> -o type=<target_qos> for cloning where it's almost always useful.