There are changes made to the original design in the approved
Cinder spec on over subscription in thin provisioning during
the review process of the code submission. Now the code is merged,
the spec should be updated to reflect the changes.
Change-Id: I765af2e69f8b7dedf078f35a2c0354aaf9f5c00e
blueprint: over-subscription-in-thin-provisioning
ec00b7b674