Fix broken behaviour when given append parameter.

Fix broken behaviour when given append parameter.

This patch makes it so that Lua now goes straight into interactive
mode when not given initrd as a parameter; previosuly it was assuming
that the --append parameter was a file name to be read and executed,
which was broken.

Signed-off-by: Felipe Huici <felipe.huici@neclab.eu>
Reviewed-by: Simon Kuenzer <simon.kuenzer@neclab.eu>