PR geerlingguy#83: Adjust docs for elasticsearch_package.

Merge pull request geerlingguy#78 from midgleyc/fix-elasticsearch-6-d…

…eployment

Fix elasticsearch 6 deployment

Fixes geerlingguy#70: Use jvm options override file instead of overri…

…ding entire jvm.options file.

PR geerlingguy#54 follow-up: Formatting in README.

Add required gnupg2 dependency for Ubuntu 18.04.

Fixes geerlingguy#53: Changing configuration didn't restart elasticse…

…arch.

Fixes geerlingguy#52: Update default version to 7.x.

PR geerlingguy#42 follow-up: Configure JVM heap size.

Fixes geerlingguy#39: Fix hanging when certain types of elasticsearch…

… config is changed.

Fix failing tests on Elasticsearch 6.x.