While that repository is used to provision the buildfarm machine it hasn’t been actively used for a long time. Initially we have provisioned the official buildfarm with those scripts but since then we have only updated it but never used the code to provision a new buildfarm from scratch.
Currently there is some work in progress to update the deployment code to use Xenial (rather than Trusty): https://github.com/ros-infrastructure/buildfarm_deployment/pull/146 The PR is in progress though and I don’t think it is ready to be used as-is at the moment (but hopefully soon).