Fixes #3860 - automated discovery provisioning

Replaces https://github.com/theforeman/foreman_discovery/pull/97
This works if I use `debian<%= facts_hash['uniqueid'] %>` but not if I use `debian<%= @host.facts_hash['uniqueid'] %>` - would be nice if users could use the same ERB conventions they use in other places, but I don't know if that's possible? Not a big deal...