daemon/graphdriver/overlay2: set TarOptions.InUserNS for native differ

Commits b2fd67de77 (and the follow-up commit
f6b80253b8) updated doesSupportNativeDiff to
detect whether the host can support native overlay diffing with userns
enabled.

As a result, [useNaiveDiff] would now return "false" in cases where it
previously would return "true" (and thus skip). However, [overlay2],
unlike [fuse-overlay] did not take user namespaces into account, when
using the native differ, and it therefore did not set the InUserNS option
in TarOptions.

As a result pkg/archive.createTarFile would attempt tocreate [device-nodes]
through [handleTarTypeBlockCharFifo] which would fail, but the resulting
error `EPERM` would be discarded, and `createTarFile` would not return
early, therefor attempting to [os.LChown] the missing file, ultimately
resulting in an error:

    failed to Lchown "/dev/console" for UID 0, GID 0: lchown /dev/console: no such file or directory

This patch fixes the missing option in overlay.

[useNaiveDiff]: 47eebd718f/daemon/graphdriver/overlay2/overlay.go (L248-L256)
[overlay2]: 47eebd718f/daemon/graphdriver/overlay2/overlay.go (L684-L689)
[fuse-overlay]: 47eebd718f/daemon/graphdriver/fuse-overlayfs/fuseoverlayfs.go (L456-L462)
[device-nodes]: ff1e2c0de7/pkg/archive/archive.go (L713-L720)
[handleTarTypeBlockCharFifo]: 47eebd718f/pkg/archive/archive_unix.go (L110-L114)
[os.LChown]: ff1e2c0de7/pkg/archive/archive.go (L762-L773)

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/overlay2/overlay.go

@@ -14,6 +14,7 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/containerd/containerd/pkg/userns"
 	"github.com/containerd/continuity/fs"
 	"github.com/containerd/log"
 	"github.com/docker/docker/daemon/graphdriver"
@@ -678,7 +679,6 @@ func (d *Driver) ApplyDiff(id string, parent string, diff io.Reader) (size int64
 		return d.naiveDiff.ApplyDiff(id, parent, diff)
 	}
 
-	// never reach here if we are running in UserNS
 	applyDir := d.getDiffPath(id)
 
 	logger.Debugf("Applying tar in %s", applyDir)
@@ -686,6 +686,7 @@ func (d *Driver) ApplyDiff(id string, parent string, diff io.Reader) (size int64
 	if err := untar(diff, applyDir, &archive.TarOptions{
 		IDMap:          d.idMap,
 		WhiteoutFormat: archive.OverlayWhiteoutFormat,
+		InUserNS:       userns.RunningInUserNS(),
 	}); err != nil {
 		return 0, err
 	}