Let Puppet manage make.conf

There is no need to pass build options from the CI host because the
algorithm Puppet uses to make /etc/portage/make.conf works just as well
inside the container.
5 jobs for master in 58 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
canceled Build haswell-server #328
nest

00:00:58

failed Build haswell-server #322
nest

00:02:41

failed Build haswell-server #323
nest

00:11:02

failed Build haswell-server #324
nest

00:02:47

passed Build haswell-server #325
nest

00:16:10