By default, when the service stops or starts, the generated init scripts remove the container, but not the associated volumes. 
To change this behaviour, add the following code to the manifest file:
docker::run { 'helloworld':
  remove_container_on_start => true,
  remove_volume_on_start    => false,
  remove_container_on_stop  => true,
  remove_volume_on_stop     => false,
}
This should do!