[Cleanup] Clean up elasticsearch role

Don't compare with empty string

Explicitly checkout master branch of head repository.

Space after variable name

elasticsearch/tasks/datadir.yml

@@ -16,7 +16,7 @@
   tags:
     - elasticsearch
   when:
-    - elasticsearch_custom_datadir != ''
+    - elasticsearch_custom_datadir
     - elasticsearch_custom_datadir != None
 
 - name: Datadir is moved to custom path
@@ -44,7 +44,7 @@
   tags:
     - elasticsearch
   when:
-    - elasticsearch_custom_datadir != ''
+    - elasticsearch_custom_datadir
     - elasticsearch_custom_datadir != None
     - elasticsearch_custom_datadir != elasticsearch_current_real_datadir_test.stdout
     - not elasticsearch_custom_datadir_test.stat.exists

elasticsearch/tasks/plugin_head.yml

@@ -15,6 +15,7 @@
         repo: "https://github.com/mobz/elasticsearch-head.git"
         dest: "{{ elasticsearch_plugin_head_clone_dir }}"
         clone: yes
+        version: master
       tags:
         - packages
 

elasticsearch/tasks/tmpdir.yml

@@ -54,4 +54,4 @@
       tags:
         - elasticsearch
       when: elastic_stack_version is version('6', '>=')
-  when: (elasticsearch_custom_tmpdir != '' and elasticsearch_custom_tmpdir != None) or fstab_tmp_noexec.rc == 0
+  when: (elasticsearch_custom_tmpdir and elasticsearch_custom_tmpdir != None) or fstab_tmp_noexec.rc == 0

java/tasks/openjdk.yml

@@ -15,7 +15,7 @@
 
 - name: Install openjdk package
   apt:
-    name: "openjdk-{{ java_version}}-jre-headless"
+    name: "openjdk-{{ java_version }}-jre-headless"
     default_release: "{{ java_apt_release }}"
     state: present
   tags: