Let def.json variables be defined based on classes, particularly from "policy_server"

We would like certain settings, such as schedule and splaytime, to be different between the policy-hub and clients.

"def.json" is read very early in the start-up process (and rightly so), so it is understandable that it cannot have full access to a site's own policy classes which are read much later.  Nevertheless the particular classes "policy_server" and "am_policy_hub" seem to be decided very close to "def.json", so might be amenable to some sort of refactoring.  (See "cf-agent -v" output on a hub.)

Could consideration be given to enabling "def.json" to handle early classes such as "policy_server"?