Allow for self-signed certificate customizations

Description

The Onionspray Ansible Role customizing the make-selfsigned-wildcard-ssl-cert.sh script.

But that could be done with a configuration file, without changing files tracked by Git, which also simplifies the needed Ansible logic.

Tasks

• Implement a configuration file for make-selfsigned-wildcard-ssl-cert.sh.
• Take the opportunity to improve the script's coding standards.

Time estimation

• Complexity: very small (0.5 day)
• Uncertainty: low (x1.1)
• Reference (adapted)