rootfs: use new ctx to cleanup instead of canceled one
rootfs: use new ctx to cleanup instead of canceled one

rootfs.CreateDiff might be canceled by context for some reason. Based on
this case, the defer function should use the new ctx to do cleanup
temporary snapshotter instead of the canceled one.

Signed-off-by: Wei Fu <df4176d36abdc6fd0d966de5d5471522668de494@gmail.com>

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