I back ported that patch to 18.2 from the tag. Then ran gradle, and created a new RPM package. So I'm good to go on that data path issue. BTW: The gradle build is smooth, and painless. Only took me about 10 minutes to cherry-pick the commit from git, and repackage the whole application. Good work.
My issue was my init.d script. I have not checked it in a while, and it was setting a default "ES_WORK / ES_PATH" environment variable. This was overriding my configuration in elasticsearch.yml. Once I removed the environment variables from the init script, everything was good to go.
I used debug logging on env to find out what values it was setting. Then I traced it down to my init script.