Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
Uses standard NixOS user config merging.
Work in progress: The slave config does not actually start the slave agent. This just configures a
jenkins user if required. Bare minimum to enable a nice jenkins SSH slave.
