Change certname from ci to builder

CI is jargon.

Containerfile

@@ -9,7 +9,7 @@ ARG PROFILE
 RUN eix-sync -q
 
 # Configure locales and set up some conveniences
-RUN puppet agent --test --certname ci --environment main --tags nest::base::distcc,nest::base::locale,nest::base::portage,nest::base::puppet --logdir /var/log/puppet --rundir /var/run/puppet --vardir /var/lib/puppet --runtimeout 0; [ $? -eq 2 ]
+RUN puppet agent --test --certname builder --environment main --tags nest::base::distcc,nest::base::locale,nest::base::portage,nest::base::puppet --logdir /var/log/puppet --rundir /var/run/puppet --vardir /var/lib/puppet --runtimeout 0; [ $? -eq 2 ]
 
 # Locale is managed by Puppet, but
 # it also needs to be persisted in the image.