add for V1 config format tests

Recently, Hatohol project Wiki's [log search system description](https://github.com/project-hatohol/hatohol/wiki/Log-search) updates for `td-agent2` with `--use-v1-config` option.
For now, `fluent-plugin-groonga` is lack of test(s) for V1 config format.
So, I added tests for V1 format config tests.
Why don't you add tests for V1 config format tests?