Enable ZooKeeper 4 letter words

So that tests which use ZooKeeper can issue the 4-letter-word
debug commands, make sure they are enabled in the zoo.cfg file.

Change-Id: Ib614e918e02306564c2ed6adb4ec350e40df9043

roles/ensure-zookeeper/tasks/main.yaml

@@ -46,6 +46,12 @@
     mode: 0644
   become: true
 
+- name: Enable ZooKeeper 4lw
+  lineinfile:
+    path: /opt/zookeeper/conf/zoo.cfg
+    line: "4lw.commands.whitelist=*"
+  become: true
+
 - name: Setup ZooKeeper TLS
   include_tasks: ./setup_tls.yaml
   when: zookeeper_use_tls