QemuOpts: add qemu_opts_append to replace append_option_parameters For later merge .create_opts of drv and proto_drv in qemu-img commands. Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Leandro Dorileo <l@dorileo.org> Signed-off-by: Chunyan Liu <cyliu@suse.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>