Perform Operator level Security Health check for Keystone

Perform Operator level Security Health check for Keystone:
 - check file permission and ownership for keystone configuration files
 - check for existence of admin token in /etc/keystone/keystone.conf
 - check for existence of AdminTokenAuthMiddleware in /etc/keystone/keystone-paste.ini
 - check for keystone TLS enablement
   - check for file permission and file ownership for TLS certificate, private key and RootCA