Added support for optionally creating the elasticsearch user and group before installing elasticsearch.

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.

tasks/elasticsearch-optional-user.yml

@@ -0,0 +1,18 @@
+---
+#Add the elasticsearch user before installing from packages.
+- name: Ensure optional elasticsearch group is created with the correct id.
+  group:
+    state: present
+    name: "{{ es_group }}"
+    system: yes
+    gid: "{{ es_group_id }}"
+
+- name: Ensure optional elasticsearch user is created with the correct id.
+  user:
+    state: present
+    name: "{{ es_user }}"
+    comment: elasticsearch system user
+    system: yes
+    createhome: no
+    uid: "{{ es_user_id }}"
+    group: "{{ es_group }}"