add new extrausers command passwd-expire

add new extrausers command passwd-expire

This enhances extrausers with a new passwd-expire command that causes
a local user's password to be expired as if the `passwd --expire`
command was run, so the password needs to be changed on initial login.

Example: EXTRA_USERS_PARAMS += " useradd ... USER; passwd-expire USER;"

Tested: on useradd accounts
When configured with Linux-PAM, console login prompts for and can
successfully change the password.  OpenSSH server works.  Dropbear
SSH server notes the password must be changed but does not offer a
password change dialog and rejects the login request.

Signed-off-by: Joseph Reynolds <joseph-reynolds@charter.net>
Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>