os: Only enable debian-stanford backport for Wheezy and Jessie

templates/os/sources/stanford.list.erb

@@ -24,7 +24,7 @@ deb-src http://debian.stanford.edu/debian-stanford <%= dist %> main non-free con
 # The Stanford restricted Debian archive and source tree.
 deb     http://debian.stanford.edu/debian-local <%= dist %> main non-free contrib
 deb-src http://debian.stanford.edu/debian-local <%= dist %> main non-free contrib
-<% if @lsbdistcodename != 'lenny' && @lsbdistcodename != 'jessie' -%>
+<% if @lsbdistcodename == 'wheezy' || @lsbdistcodename == 'jessie' -%>
 
 # Additional Stanford-local backports.
 deb     http://debian.stanford.edu/debian-stanford <%= dist %>-backports main non-free contrib