c224edc5c6
`OverlayConvertWhiteout` calls `mknod c 0 0` which is not allowed when running in a user namespace, even in Ubuntu kernel. Although there is an alternative hacky way to create whiteouts without calling mknod as Moby `overlay2` actually does(see #3762), let's use naive applier when running in UserNS and call it a day. Close #3762 Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>