Put cinder rootwrap config in separate function

Separate out Cinder's rootwrap configuration so that it can be called
from Grenade's upgrade scripts. This follows the same model as Nova uses
with configure_nova_rootwrap() which can be called from Grenade to
refresh rootwrap config.

Change-Id: Id808abc2b5754443362b3de4b3453e305d3720f3
Merge "Put cinder rootwrap config in separate function"