test-loop-block: also test dissection without ADD/PIN of partition block devices
    
    Let's extend the test further, and try the codepaths where we do not
    pin/add the partition block devices (i.e. which is the codepaths we use
    when running without privs)
    
    (cherry picked from commit 9f2d9a4aaba63d3b93d72e776413c8ed5c86e3fb)