Implement aodh 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: I7112e8c9186b1266a73bab98cf5f3831123cb703
Related-Prod: PROD-22099
diff --git a/tests/pillar/server_cluster.sls b/tests/pillar/server_cluster.sls
index d49cfd7..549f916 100644
--- a/tests/pillar/server_cluster.sls
+++ b/tests/pillar/server_cluster.sls
@@ -44,6 +44,17 @@
       password: test
     notifications:
       store_events: default
+    cache:
+      engine: memcached
+      members:
+      - host: 127.0.0.1
+        port: 11211
+      - host: 127.0.0.1
+        port: 11211
+      security:
+        enabled: true
+        strategy: ENCRYPT
+        secret_key: secret
 apache:
   server:
     enabled: true