add ansible var for ES_TMPDIR env var (#714)

Elasticsearch requires its temp directory to be mounted as executable (see executable-jna-tmpdir). However, the CIS guidelines (e.g., CIS_Red_Hat_Enterprise_Linux_7_Benchmark_v2.1.1, 1.1.5) recommend mounting /tmp with noexec. Therefore, users of this ansible role may have reason to set elasticsearch's temp dir to a non-default location.

(The elasticsearch environment variable ES_TMPDIR gets set to /tmp by default. This PR preserves this default behavior.)

defaults/main.yml

@@ -26,6 +26,7 @@ es_config_jvm: "jvm.options.j2"
 #Need to provide default directories
 es_conf_dir: "/etc/elasticsearch"
 es_pid_dir: "/var/run/elasticsearch"
+es_tmp_dir: "/tmp"
 es_data_dirs:
   - "/var/lib/elasticsearch"
 es_log_dir: "/var/log/elasticsearch"

templates/elasticsearch.j2

@@ -5,6 +5,9 @@
 # Elasticsearch home directory
 ES_HOME={{es_home}}
 
+# Elasticsearch temp directory
+ES_TMPDIR={{ es_tmp_dir }}
+
 # Elasticsearch Java path
 {% if es_java_home | length > 0 %}
 JAVA_HOME={{ es_java_home }}