Implement neutron 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: I7f623586023c8b0605bb77977a28d6b7c47e5287
Related-Prod: PROD-22099
3 files changed