Propose: Add QoS capability to the IBM Storwize driver

Storwize storage can configure I/O throttling rate to enable to QoS. This
feature can be implemented for Storwize driver.

Related blueprint: cinder-storwize-driver-qos

Change-Id: I1323591bfa0ca25ede5dc7c376bad4eeca572f1e
Merge "Propose: Add QoS capability to the IBM Storwize driver"