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
3 files changed