systemd: fix wrong nobody-group assignment

systemd: fix wrong nobody-group assignment

The generated /etc/group file had a wrong group name for nobody-group
which was nobody with same id as nogroup groupd. This was leading to
duplcate groups, with same ids and different names.

More can be read on this link:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=11766

Signed-off-by: Piotr Łobacz <p.lobacz@welotec.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>