openssh: Tweak sshd_config to tackle for PAM taking care of authentication

We sort of disable clear text PasswordAuthentication
pam does not like it

Signed-off-by: Khem Raj <raj.khem@gmail.com>
libpam: Disable nullok_secure

This will let us ssh with empty password as root user.
Its less secure but good for development work.

Signed-off-by: Khem Raj <raj.khem@gmail.com>