Avoid to stumble over missing /dev/stderr in boot script started by systemd

... as systemd uses socketpair() to create create a pair of connected sockets
instead of using pipe() or a pty/tty pair.  In comparision to a pipe or a
pseudo terminal line it is currently impossible to dup the file descriptor of
a socket.

Signed-off-by: Werner Fink <werner@suse.de>