Add pretasks to exit quick when needed

The journalbeat playbook uses conditionals to know when to deploy the
journalbeat collector. This change makes it so the playbook simply exits
when the journal is not found or the environment being deployed is not
using systemd. This change will result in faster deployments in mixed
environments as the role will no longer need to iterate over its
conditional.

Change-Id: I581b61902723f54237623036566a83c9be79210e
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>

elk_metrics_6x/installJournalbeat.yml

@@ -56,11 +56,14 @@
       tags:
         - always
 
+    - name: Halt this playbook if no journal is found
+      meta: end_play
+      when:
+        - not (journal_dir.stat.exists | bool) or
+          (ansible_service_mgr != 'systemd')
+
   roles:
     - role: elastic_journalbeat
-      when:
-        - journal_dir.stat.exists | bool
-        - ansible_service_mgr == 'systemd'
 
   tags:
     - beat-install
@@ -76,11 +79,22 @@
 
   environment: "{{ deployment_environment_variables | default({}) }}"
 
+  pre_tasks:
+    - name: Check for journal directory
+      stat:
+        path: /var/log/journal
+      register: journal_dir
+      tags:
+        - always
+
+    - name: Halt this playbook if no journal is found
+      meta: end_play
+      when:
+        - not (journal_dir.stat.exists | bool) or
+          (ansible_service_mgr != 'systemd')
+
   roles:
     - role: elastic_rollup
-      when:
-        - journal_dir.stat.exists | bool
-        - ansible_service_mgr == 'systemd'
       index_name: journalbeat
 
   tags: