[4.14.0] no support for module enable

[tuxmaster5000]

Under filebeat 8 the modules under /etc/filebeat/modules.d are disabled by default, and needs to be enabled via
filebeat modules enable <module>

[TuningYourCode]

We use filebeat 7.x modules just fine by https://github.com/pcfens/puppet-filebeat/blob/master/manifests/init.pp#L117

e.g.:

filebeat::modules:
  mysql:
    error:
      enabled: true
      var.paths:
        - /var/log/mysql/error.log
    slowlog:
      enabled: true
      var.paths:
        - /var/log/mysql/slow.log
  nginx:
    access:
      enabled: true
    error:
      enabled: true
      var.paths:
        - /var/log/nginx/*.error.log
  system:
    syslog:
      enabled: true
      var.paths:
        - /var/log/syslog
    auth:
      enabled: true
      var.paths:
        - /var/log/auth.log
filebeat::overwrite_pipelines: true
filebeat::setup:
  ilm:
    enabled: true
    overwrite: true
  dashboards:
    enabled: true
  template:
    settings:
      index:
        number_of_replicas: 0