[server] Add SSL certificate creator

It is a convenient script for creating a SSL supported RabbitMQ
environment.

This script is based on RabbitMQ's SSL configuration document:
https://www.rabbitmq.com/ssl.html

The script creates the following:

  * CA
  * Server certificate
  * Client certificate

RabbitMQ uses CA's certificate and server certificate.

Hatohol HAPI JSON and fluent-plugin-hatohol uses CA's certificate and
client certificate.
Merge pull request #395 from project-hatohol/add-ssl-certificate-creator

[server] Add SSL certificate creator