libgfs2: Push down build_per_node() into the utils
    
    The trouble with having this function in libgfs2 is that it creates
    per_node and everything inside it, which means that it's difficult to
    know where an error occurred and we don't have any control over how
    debug/error messages are printed. It's also not necessarily the order
    that we want to create the inodes in all utilities. Move
    build_per_node() down into the utils and add error reporting to match.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>