nspawn: move payload to sub-cgroup first, then sync cgroup trees
    
    if we sync the legacy and unified trees before moving to the right
    subcgroup then ultimately the cgroup paths in the hierarchies will be
    out-of-sync... Hence, let's move the payload first, and sync then.
    
    Addresses: https://github.com/systemd/systemd/pull/9762#issuecomment-441187979
    (cherry picked from commit 27da7ef0d09e00eae821f3ef26e1a666fe7aa087)
    
    Resolves: #1837094
    
    patch_name: 0374-nspawn-move-payload-to-sub-cgroup-first-then-sync-cg.patch
    present_in_specfile: true
    location_in_specfile: 374
    squash_commits: true