sulogin: improve support for locked root account

sulogin: improve support for locked root account

Some installations and distributions don't use a root account password
for security reasons and use sudo instead. In that case, asking for the
password makes no sense, and it is not even considered as valid as it's just
"*" or "!".

In these cases --force is required to just start a root shell and no
ask for password.

I don't think it's a good idea to automatically start root shell when
locked account is detected. It's possible that the machine is on
public place and for example Ubuntu uses root account disabled by
default (and also Fedora when installed by yum/dnf without anaconda).

The --force option forces admins to think about it...

The distro maintainers can also use --force in their initscripts or
systemd emergency.service if they believe that promiscuous setting is
the right thing for the distro.

Addresses: https://bugs.debian.org/326678
Signed-off-by: Karel Zak <kzak@redhat.com>