Added server_id variable to postfix config file templates.

install/tpl/mysql-virtual_domains.cf.master

install/tpl/mysql-virtual_email2email.cf.master

install/tpl/mysql-virtual_forwardings.cf.master

install/tpl/mysql-virtual_mailboxes.cf.master

install/tpl/mysql-virtual_recipient.cf.master

install/tpl/mysql-virtual_sender.cf.master

install/tpl/mysql-virtual_transports.cf.master