Add missing stdlib fixture

[arioch]

This PR fixes:

.......F..

Failures:

  1) motd On Debian based    Operating Systems When dynamic motd is false should contain File_line[dynamic_motd] with line => "session    optional     pam_motd.so  motd=/run/motd.dynamic noupdate"
     Failure/ Error: it { should contain_file_line('dynamic_motd').with_line('session    optional     pam_motd.so  motd=/run/motd.dynamic noupdate') }
     Puppet::Error:
       Puppet::Parser::A    ST::Resource failed with error ArgumentError: Invalid resource type file_line at motd/spec/fixtures/modules/motd/manifests/init.pp:45 on node buildserver
     # ./spec/classes /motd_spec.rb:90:in `block (4 levels) in <top (required)>'

Finished in 0.62725 seconds
  110 examples, 1 failure