shadow: 'useradd' copies root's extended attributes

shadow: 'useradd' copies root's extended attributes

The copy of extended attributes is interesting for
Smack systems because it allows to set the security
template of the user's home directories without
modifying the tools (useradd here). But the version
of useradd that copies the extended attributes doesn't
copy the extended attributes of the root. This can make
use of homes impossible! This patch corrects the issue
by copying the extended attributes of the root.

This includes 2 patches to implement the behaviour:
one for the target and one for the native.

The patch for the target was submitted upstream (see below)
The patch for the native couldn't be submitted upstream
because it applies on a patch specific to open-embedded
(that was refused upstream).

Upstream-Status: Submitted (http://lists.alioth.debian.org/pipermail/pkg-shadow-commits/2017-March/003804.html)

Change-Id: I7ced318a02206fd3f15a6995f59bb82b6c6453d5
Signed-off-by: José Bollo <jose.bollo@iot.bzh>
Signed-off-by: Stephane Desneux <stephane.desneux@iot.bzh>