fix(init) ensure DAO init errors are correctly reported

Since they are tables in the old DAO, this would fail with a super-sed:
error "bad argument #2 to 'assert'"

kong/init.lua

@@ -157,7 +157,11 @@ function Kong.init()
   local config = assert(conf_loader(conf_path))
 
   local dao = assert(DAOFactory.new(config)) -- instantiate long-lived DAO
-  assert(dao:init())
+  local ok, err_t = dao:init()
+  if not ok then
+    error(tostring(err_t))
+  end
+
   assert(dao:are_migrations_uptodate())
 
   -- populate singletons