Rename entrypoint server from 'rebond' to 'bastion'
Add key servers to infrastructure :
  - bastion : uniq ssh entrypoint
  - nat : route all http req (apt-get, etc...) from private subnets to internet
Add sample servers for config example and tests purpose
Variables are now on a separate file
Each layout has his own network :
first octet "10"
second octet represent the layout => "10", "20", "11", "22"