Uses oslo.imageutils

Commit 035668 had the QemuImgInfo class moved to Oslo.
This class diverged from Nova and then missed some changes
made in Nova since then. The two projects will be able to use
identical classes by adapting imageutils.

Change-Id: I6ed352c42e45d32de94066c82f83e7332d4a98ed
Merge "Uses oslo.imageutils"