xpack features refactoring (#653)

- rename es_enable_xpack variable to oss_version
  this variable name should be more explicit and consistent with the xpack changes made in 6.3
  es_enable_xpack can still be used but is deprecated and will be removed in a later version.
- remove es_xpack-features variables
  this variable was not working anymore since 6.3 [0]

[0]: https://github.com/elastic/ansible-elasticsearch/issues/608

tasks/elasticsearch-parameters.yml

@@ -1,5 +1,10 @@
 # Check for mandatory parameters
 
+- name: Warn about deprecated  es_xpack_features variable
+  debug:
+    msg: "WARNING: es_xpack_features variable is now deprecated. All feature are now enabled by default"
+  when: es_xpack_features is defined and not oss_version
+
 - name: fail when es_proxy_port is not defined or is blank
   fail: msg="es_proxy_port must be specified and cannot be blank when es_proxy_host is defined"
   when: (es_proxy_port is not defined or es_proxy_port == '') and (es_proxy_host is defined and es_proxy_host != '')
@@ -13,8 +18,8 @@
 - name: fail when api credentials are not declared when using security
   fail: msg="Enabling security requires an es_api_basic_auth_username and es_api_basic_auth_password to be provided to allow cluster operations"
   when:
-    - es_enable_xpack and "security" in es_xpack_features
-    - es_api_basic_auth_username is not defined
+    - not oss_version
+    - es_api_basic_auth_username is defined
     - es_api_basic_auth_password is not defined
 
 - name: fail when ssl enabled without defining a key and certificate
@@ -38,4 +43,3 @@
 
 - name: set fact use_system_d
   set_fact: use_system_d={{(ansible_distribution == 'Debian' and ansible_distribution_version is version('8', '>=')) or (ansible_distribution in ['RedHat','CentOS'] and ansible_distribution_version is version('7', '>=')) or (ansible_distribution == 'Ubuntu' and ansible_distribution_version is version('15', '>=')) }}
-