cloud: drop VMDK output image for cloud
    
    We added this so we could eventually use the VMDK to optimize our
    uploads to AWS but it turns out the VMDK created by imagefactory
    isn't in the right format anyway.
    
    ```
    SNAPSHOTTASKDETAIL      0.0     VMDK    deleted ClientError: Disk validation failed [Unsupported VMDK File Format]
    ```
    
    Let's drop them for now.
    
    Signed-off-by: Dusty Mabe <dusty@dustymabe.com>