test/rauc.t: add basic test for --casync-args convert option
test/rauc.t: add basic test for --casync-args convert option

Signed-off-by: Christopher Obbard <0becaf7888cff31ba54e40b1ffb8263e09b8b7da@collabora.com>

ejoerns/rauc,rauc/rauc,rauc/rauc,jluebbe/rauc,jluebbe/rauc,jluebbe/rauc,ejoerns/rauc,rauc/rauc,ejoerns/rauc