(#5150) Make fact REST terminus configurable to connect to inventory service

Puppet masters can now set the inventory_server and inventory_port
option to point to another puppet master that will function as the
central inventory service. When agents connect to the
puppet master, this will send fact data from the puppet master over REST
to the inventory service.

The puppet master itself will still store the client fact data in the
local yaml dir by setting the cache class to yaml.

Getting puppet masters to talk to each other using certs is difficult.

Paired-with: Jesse Wolfe <jesse@puppetlabs.com>