Implement heat 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: Ice0259e12009bddec2607d54219e1d4b639839c2
Related-Prod: PROD-22099
diff --git a/tests/pillar/server_cluster.sls b/tests/pillar/server_cluster.sls
index 2cb36a2..0b28922 100644
--- a/tests/pillar/server_cluster.sls
+++ b/tests/pillar/server_cluster.sls
@@ -69,3 +69,16 @@
       'cloudformation:DescribeStackResource':
     max_stacks_per_tenant: 150
     max_nested_stack_depth: 10
+    cache:
+      engine: memcached
+      members:
+      - host: 127.0.0.1
+        port: 11211
+      - host: 127.0.1.1
+        port: 11211
+      - host: 127.0.2.1
+        port: 11211
+      security:
+        enabled: true
+        strategy: ENCRYPT
+        secret_key: secret