Raise priority of environment (!?)

WARNING: I am not sure about this.

*Issue*: we are defining `logstash::defaultsfiles` in both the `role-monitoring.yaml` file and in our `environment.yaml` specific files. Based on the hiera hierachy, we will never take into account our environment specific setting.

*Resolution*: I've switched the hierarchy so environment specific variables take precedence over the roles. Let me know if that is a terrible idea.