Implement gnocchi memcache security strategy

Provides an option to authenticate and optionally encrypt the token
data stored in the cache:

memcache_security_strategy = MAC/ENCRYPT
memcache_secret_key = secret_key

Change-Id: I740b49e9626435348e0c0c9e665ac04c60ba1583
Related-Prod: PROD-22099
diff --git a/tests/pillar/server_cluster.sls b/tests/pillar/server_cluster.sls
index 8cdcf25..b9f1415 100644
--- a/tests/pillar/server_cluster.sls
+++ b/tests/pillar/server_cluster.sls
@@ -58,6 +58,10 @@
         port: 11211
       - host: 127.0.3.1
         port: 11211
+      security:
+        enabled: true
+        strategy: ENCRYPT
+        secret_key: secret
     metricd:
       workers: 5
   statsd:
@@ -108,4 +112,4 @@
     pkgs:
       - apache2
     modules:
-      - wsgi
\ No newline at end of file
+      - wsgi