yast: Fallback to DES without configuration in /etc/login.def

yast2-security didn't use secure defaults to protect passwords. This became a problem on 2019-10-07 when configuration files that set secure settings were moved to a different location. As of the 20191022 snapshot the insecure default settings were used until yast2-security switched to stronger defaults in 4.2.6 and used the new configuration file locations. Password created during this time used DES password encryption and are not properly protected against attackers that are able to access the password hashes.