Add strict_variables support when puppetdb is not on puppetmaster

When using the new `strict_variables` feature of puppet 3.5, including `puppetdb::master::config` on the puppetmaster fails with `Undefined variable "puppetdb::disable_ssl"` because `Class[puppetdb]` is not declared and so `puppetdb::disable_ssl` is not defined if puppetdb and puppetmaster are not on the same machine.