added container:attach() into the Lua API

lua-lxc: added container:attach(...) binding into the Lua API
Signed-off-by: Bree <ashtoreth@ukr.net>

I don't think you need both i and j here, just i. The code you likely got this from (container_start()) needed both because in it's case sometimes j was not incremented in the loop. You can just assign using argv[i] = strdupa(arg).