Add support for the akanda raw image

Check if a qcow2 image is already present locally to be used,
otherwise default to the iso.

Change-Id: I20223b965e2d7b26e7d2559ce9f6d75f88f3016f
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>
Merge pull request #21 from rodis/feature/add-raw-image-support

Add support for the akanda raw image