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
4 files changed