* Make the upstream in route53 plugin optional.
Signed-off-by: Jiacheng Xu <xjcmaxwellcjx@gmail.com>

* Add 2 tests for upstream in route53.
Signed-off-by: Jiacheng Xu <xjcmaxwellcjx@gmail.com>

* Change the readme.
Signed-off-by: Jiacheng Xu <xjcmaxwellcjx@gmail.com>