pipelines.yml ignored on logstash systemd service

For all general issues, please provide the following details for fast resolution:

- Version: 6.0
- Operating System: CentOS 7
- Steps to Reproduce: create pipelines.yml and run logstash as a service
pipelines.yml is ignored completely
See [this thread](https://discuss.elastic.co/t/pipelines-yml-ignored-on-logstash-running-as-a-service/107828/8) for additional questions/answers as well as troubleshooting steps

/etc/logstash/logstash.yml has path.config commented out
regular execution of logstash (no service) reads pipelines.yml but running logstash as a service ignores it. Logstash log file shows nothing is even trying to read pipelines.yml