postfix: Fix postfix_relayhost condition

The 'bool' filter only accepts some strings.

roles/postfix/tasks/main.yml

@@ -73,13 +73,13 @@
     - compat_maps.db
 
 - name: install extra packages for relaying via smarthost
-  when: postfix_relayhost|bool
+  when: postfix_relayhost != ""
   package:
     name: cyrus-sasl
     state: present
 
 - name: install relay_passwords file
-  when: postfix_relayhost|bool
+  when: postfix_relayhost != ""
   template:
     src: relay_passwords.j2
     dest: /etc/postfix/relay_passwords
@@ -91,7 +91,7 @@
 
 - name: create user account on orion to relay with
   delegate_to: orion.archlinux.org
-  when: postfix_relayhost|bool
+  when: postfix_relayhost != ""
   user:
     name: "{{inventory_hostname_short}}"
     comment: "SMTP Relay Account for {{inventory_hostname}}"