review fix for #56: add grants for guest user

Author: nurzhan-saktaganov

tests/tnt/storage.lua

@@ -85,6 +85,8 @@ box.once("testapp:schema:1", function()
     box.schema.role.grant('public', 'execute', 'function', 'raise_luajit_error')
     box.schema.func.create('raise_client_error')
     box.schema.role.grant('public', 'execute', 'function', 'raise_client_error')
+
+    box.schema.user.grant('guest', 'super')
 end)