Create hiera service_enabled keys for enabled services

Create hiera service_enabled keys for enabled services

This adds a list of all enabled service_names in the
enabled_services key, and also generates some boolean
values e.g service_name_enabled, which is more convenient
for some usage (such as haproxy where we need an easy way to
set a flag saying if a given service is enabled)

Partially-Implements: blueprint custom-roles
Change-Id: I62273f403838893602816204d9bc50d516c0057f