Increase vm.max_map_count on elasticsearch nodes

When using newer Elasticsearch versions you will receive the following error
when trying to start: elasticsearch | max virtual memory areas
vm.max_map_count [65530] likely too low, increase to at least [262144]

This could be solved by increasing the vm.max_map_count value via sysctl.

Reference: https://www.elastic.co/guide/en/elasticsearch/reference/current/vm-max-map-count.html

Change-Id: I9fa7b0222104d68bdfc838637acf5e36c479e6b2
Closes-bug: #1719528

ansible/roles/elasticsearch/tasks/config.yml

@@ -1,4 +1,12 @@
 ---
+- name: Setting sysctl values
+  sysctl: name={{ item.name }} value={{ item.value }} sysctl_set=yes
+  with_items:
+    - { name: "vm.max_map_count", value: 262144}
+  when:
+    - set_sysctl | bool
+    - inventory_hostname in groups['elasticsearch']
+
 - name: Ensuring config directories exist
   file:
     path: "{{ node_config_directory }}/{{ item.key }}"