Implement aodh 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: I7112e8c9186b1266a73bab98cf5f3831123cb703
Related-Prod: PROD-22099
3 files changed