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>
    (cherry picked from commit b4b0781b789edd4ec7d1a5a70a42776fc2b46304)