postfix: set home dir to /

For relay host users created on orion set the home directory to /
instead of the default /home/{{inventory_hostname_short}} which is not
created which makes shadow.service fail on orion.

roles/postfix/tasks/main.yml

@@ -101,6 +101,7 @@
     password: "{{ postfix_relay_password | password_hash('sha512') }}"
     shell: /sbin/nologin
     update_password: always
+    home: / # Set home directory so shadow.service does not fail
     create_home: no
 
 - name: open firewall holes