Implement glance 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: I1ba1f4fa61684d3dd5f0aa1478044e0f46b7cffc
Related-Prod: PROD-22099
diff --git a/tests/pillar/cluster.sls b/tests/pillar/cluster.sls
index b06af82..b207e46 100644
--- a/tests/pillar/cluster.sls
+++ b/tests/pillar/cluster.sls
@@ -58,3 +58,16 @@
       image_tag: 256
       image_location: 15
       user_storage: 0
+    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