mod_external_services: Also validate services added by other modules This ensures that problems with entries added other modules, e.g. mod_turn_external, are reported on startup. However, this depends on load order and whether a `module:depends()` call comes before the `module:add_item()` call. A followup commit will do something about that.

describe("util.poll", function ()
	it("loads", function ()
		require "util.poll"
	end);
end);