snapshots/native: ignore xattr errors during CopyDir
snapshots/native: ignore xattr errors during CopyDir

`secuity.*` xattrs cannot be copied in most cases

For moby/buildkit#1189

Signed-off-by: Akihiro Suda <10ddef0dea2a66ab193b07198faa879adcb213d8@hco.ntt.co.jp>

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