Heap dump path

[martinb3]

Heap dump path default

Previous versions of Elasticsearch did not configure the JVM heap dump path. As such, the JVM would default to the working directory for the JVM. For the RPM and Debian package distributions this was a problem because the default would be /usr/share/elasticsearch, a path not writable by the elasticsearch user meaning that out of the box heap dumps would not be produced. It is a tragedy to not have this diagnostic information by default. Starting in Elasticsearch 6.0.0, the RPM and Debian packages configure the heap dump path to be /var/lib/elasticsearch. If this location is not suitable for receiving heap dumps (e.g., due to disk space concerns), you should adjust this path to a more suitable location.

The default value isn't going to work for us, because we need to parameterize it. Add back -XX:HeapDumpPath=/var/lib/elasticsearch and make it a workable parameter.