Verify installation benefits from adding -H option

[TuulaP]

The verify step requires e.g. header option -H 'Content-Type: application/json' to be added. Without it one gets an error of type:

{"error":"Content-Type header [application/x-www-form-urlencoded] is not supported","status":406}

Also for service mode the custom policy file is useful to be added to the jvm.options file of ElasticSearch 7.x ,e.g. via with line:

-Djava.security.policy=file:/etc/elasticsearch/custom-elasticsearch.policy