Use {{ mail_server_hostname }} over mail.servername

Resolves #402.

roles/mailserver/templates/etc_opendkim_TrustedHosts.j2

 {{ domain.name }}
 {% endfor %}
 {% for domain in mail_virtual_domains %}
-mail.{{ domain.name }}
-{% endfor %}
+{{ mail_server_hostname }}
+{% endfor %}

vars/defaults.yml

 # openvpn_clients: (required)
 
 # webmail
-webmail_domain: "mail.{{ domain }}"
+webmail_domain: "{{ mail_server_hostname }}"
 webmail_db_username: "roundcube"
 # webmail_db_password: (required)
 webmail_db_database: "roundcube"