fix: should get runtime name from container info
fix: should get runtime name from container info

when use `ctr t checkpoint`, runtime name should get from container
info, but not passed by flag, since task has already running with
specified runtime

Signed-off-by: Ace-Tang <a967bc6ab01ace27203ca6ab9fd77fbd3b598184@126.com>

miaoyq/containerd,thaJeztah/containerd,containerd/containerd,thaJeztah/containerd,crosbymichael/containerd,mikebrow/containerd,crosbymichael/containerd,vdemeester/containerd,estesp/containerd,miaoyq/containerd,dmcgowan/containerd,mikebrow/containerd,estesp/containerd,containerd/containerd,dmcgowan/containerd,vdemeester/containerd