Fix some defaults.

defaults/main.yml

@@ -1,13 +1,13 @@
 ---
 postfix_enabled: True
-postfix_install_packages: True
+postfix_install_packages: '{{ postfix_enabled }}'
 
 # Set it to true when you want configure your machine to send email to a relay
 postfix_relay_client: False
+postfix_use_relay_host: '{{ postfix_relay_client }}'
 postfix_relay_client_do_not_stop_submission: False
 postfix_biff: "no"
 postfix_append_dot_mydomain: "no"
-postfix_use_relay_host: True
 
 postfix_use_letsencrypt: False
 # Accepted values: none, may, encrypt