offline install using containerd runtime (#8254)

install containerd on centos need to binary download it 

but offline.yml has no that value

binary download url default in

roles/download/defaults/main.yml:runc_download_url: "https://github.com/opencontainers/runc/releases/download/{{ runc_version }}/runc.{{ image_arch }}"
roles/download/defaults/main.yml:containerd_download_url: "https://github.com/containerd/containerd/releases/download/v{{ containerd_version }}/containerd-{{ containerd_version }}-linux-{{ image_arch }}.tar.gz"

if i use default offlie.yml, it's error from task download files

because runc,containerd down url is none offline

i want fix this 

just add 2 new line