Apparently PAM reacts differently on different systems (?) and if no
authoritative matching module is found might either succeed/fail,
depending on the system.
Let's lock this down explicitly, by hooking in pam_deny.so.
Of course, these PAM files are just examples, and no distro in its right
mind would ship these unmodified, but let's default to something safe.
Fixes: #12950
Stupid PAM, please just go away!
login[26]: pam_limits(login:session): error parsing the configuration file: '/etc/security/limits.conf'
login[26]: pam_unix(login:session): session opened for user root by LOGIN(uid=0)
login[26]: Error in service module
Lennart Poettering