Make lib/cinder support both cinder-rootwrap (current case) and
oslo-rootwrap (future case) to handle the Cinder transition towards
oslo-rootwrap usage peacefully.
Related blueprint:
https://blueprints.launchpad.net/cinder/+spec/cinder-oslo-rootwrap
Change-Id: I663986304bd74cb6d72d51c553540fb5f9db1d1d