IBM Storwize driver: Retype the volume with correct empty QoS

* Currently for Storwzie driver, if the new type does not have QoS
configurations, the old QoS configurations remain in the volume after
retyping it. It should be retyped into a volume with empty QoS for the
Storwize driver.
* Refactor three dicts into one for better maintainance of the QoS keys
for Storwize driver.

DocImpact

Change-Id: I2b2801a4ef72ef02c11392ed00b56f5263a8a7e4
Closes-Bug: #1368595
Merge "IBM Storwize driver: Retype the volume with correct empty QoS"