Renamed vars, set the tasks to use the es_user and es_group vars in elasticsearch-optional-user.yml. Modifed README.md to list the es_user_id and es_group_id vars, made note that both vars are required if they are used. Removed the commented out instances of the vars in defaults/main.yml.
Added es_user, es_group, es_user_id, es_group_id vars to config testing.
Made conditionals use explicit 'is defined' test.
Add tests for es_user_id and es_group_id.
Update defaults/main.yml and test/integration/config.yml to match master plus test config additions.
