Fix broken fail2ban dovecot filter; use <HOST> instead of undocumented feature.
Fix broken fail2ban dovecot filter; use <HOST> instead of undocumented feature.

* Replace deprecated, undocumented fail2ban feature "(\P<host>\S*)" with
  supported host match "<HOST>".
* Fixes "No failure-id group in '(?: pop3-login|ima ..." fail2ban dovecot filter
  error message.
* See: https://github.com/fail2ban/fail2ban/issues/2130

tomav/docker-mailserver,tomav/docker-mailserver,tomav/docker-mailserver