(#9080) Add facts from /etc/puppetlabs/facts.d

(#9080) Add facts from /etc/puppetlabs/facts.d

This fact is a direct copy of R.I.'s work at
https://github.com/ripienaar/facter-facts

This is necessary plumbing to allow the installer to write a simple text
file based on the role the node is receiving.  For example:

    $ cat /etc/puppetlabs/facts.d/puppet_enterprise_mcollective.txt
    fact_stomp_port=61613
    fact_stomp_server=puppetmaster
    fact_is_puppetagent=true
    fact_is_puppetmaster=true

The mcollectivepe module relies on these facts being set and we need a
persistent place to write them during the interview process and later
read them when puppet agent runs to configure MCollective on the agent
systems.

Since stdlib is a public module, both /etc/facts.d and
/etc/puppetlabs/facts.d are scanned for static facts.