CORD-2457: Update head node VM config for ElasticSearch

Change-Id: I5742541ecb7e98586dd6d31774a931cc143ea867
diff --git a/prep-headnode-playbook.yml b/prep-headnode-playbook.yml
index 04c0c07..a49d2ae 100644
--- a/prep-headnode-playbook.yml
+++ b/prep-headnode-playbook.yml
@@ -66,3 +66,8 @@
   roles:
     - apache-proxy
 
+- name: Sysctl defaults
+  hosts: head
+  become: yes
+  roles:
+    - sysctl