replicate io.Copy optimizations
replicate io.Copy optimizations

Signed-off-by: Amr Mahdi <4b2905b5f8373fa9fd11ad43cde8881f1f46f498@gmail.com>

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