Install JRE headless package

Because the elasticsearch package from Elastic doesn't have a
dependency on it.

Change-Id: I416f5e7760652899f8368763a5315729fd9cccde
diff --git a/elasticsearch/map.jinja b/elasticsearch/map.jinja
index ad70680..23e2a7b 100644
--- a/elasticsearch/map.jinja
+++ b/elasticsearch/map.jinja
@@ -2,6 +2,7 @@
 Debian:
   pkgs:
   - elasticsearch
+  - default-jre-headless
   curator_pkgs:
   - python-elasticsearch-curator
   - cron