Updated PID file location to come from configuration

Partial fix for #2103 where on _NIX platforms the PID file location is hardcoded.
Now it will try and use the PID file defined in `./conf/neo4j-wrapper.conf`, or fallback to the current default of `./data/neo4j-service.pid`.
Merge pull request #2827 from Archytaus/master

Updated PID file location to come from configuration