Require monit package before attempting to manage conf.d

This fixes this:

    Error: Cannot create /etc/monit/conf.d; parent directory /etc/monit does not exist
    Error: /Stage[main]/Monit/File[/etc/monit/conf.d]/ensure: change from absent to directory failed: Cannot create /etc/monit/conf.d; parent directory /etc/monit does not exist