produce cloud image in vmdk format
This is needed for uploading the image to aws using the
github.com/coreos/mantle code base. We can upload the raw
files but it is a significant waste of bandwidth to do so.
Right now aws import-image does not support qcow2 files,
otherwise we would be using that.
Signed-off-by: Dusty Mabe <dusty@dustymabe.com>