rest_firewall: bug fix of handling an empty dict

Signed-off-by: WATANABE Fumitaka <watanabe.fumitaka@nttcom.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
rest_firewall: remove of a redundant code

Signed-off-by: WATANABE Fumitaka <watanabe.fumitaka@nttcom.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
rest_firewall: remove of an unnecessary comma of json response

Signed-off-by: WATANABE Fumitaka <watanabe.fumitaka@nttcom.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
rest_firewall: remove of unused constant values

Signed-off-by: WATANABE Fumitaka <watanabe.fumitaka@nttcom.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>