useradd-example: do not use unsupported clear text password

The clear text password support has been dropped. So let's just
use a normal ecrypted one. The password remains to be 'user3'.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit cd8232f9)
Signed-off-by: Fabio Berton <fabio.berton@criticaltechworks.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>