For basic tests it's not necessary to have the networking setup and this allows testing as a normal user as well, without root privileges. So this patch adds `--no-network` long option or `-n` short option, which allows starting QEMU without network. Cc: Yousong Zhou <yszhou4tech@gmail.com> Signed-off-by: Petr Štetiar <ynezz@true.cz>