Implement Ironic 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: Ie252472e7e000ef76660c731b293a25dc21aa433
Related-Prod: PROD-22099
diff --git a/tests/pillar/api_single.sls b/tests/pillar/api_single.sls
index 741d92b..72800fe 100644
--- a/tests/pillar/api_single.sls
+++ b/tests/pillar/api_single.sls
@@ -21,3 +21,14 @@
       password: workshop
     identity:
       engine: 'noauth'
+    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