[postfix] Deploy Postfix on mail servers (/\!\ playbook is noot ready)

Signed-off-by: Yohann D'ANELLO <ynerant@crans.org>

plays/postfix.yml

 #!/usr/bin/env ansible-playbook
 # Postfix playbook
 ---
-- hosts: sputnik.adm.crans.org, boeing.adm.crans.org, redisdead.adm.crans.org, titanic.adm.crans.org
+- hosts: postfix,!mailman
   vars:
     certbot:
       - dns_rfc2136_server: '172.16.10.147'