Harmonize consul role code

[aurelienmaury]

• check that all variables used in consul role are defined either in defaults (prefixed with hs_consul_) or vars (prefixed with __hs_consul_)
• document variable defaults that rely on the variables defined in playbook group_vars/all.yml
• document every default variable
• integrate the terraform/consul_config module into the role in files/hs_consul_config