nspawn: simplify machine terminate bus call
    
    We have the machine name anyway, let's use TerminateMachine() on
    machined's Manager object directly with it. That way it's a single
    method call only, instead of two, to terminate the machine.
    
    (cherry picked from commit 11d81e506ed68c6c5cebe319dc57a9a2fc4319c5)
    
    Resolves: #1697893
    
    patch_name: 0113-nspawn-simplify-machine-terminate-bus-call.patch
    present_in_specfile: true
    location_in_specfile: 113
    squash_commits: true