CONTEXT
apisonator does not fully support async mode yet. For context see this thread
and this JIRA

WHAT
We need to prevent HPA and Async being used in cases where Redis Sentinels is used with passwords enabled. See threescale related JIRA
Sentinels without passwords will be allowed.

HOW
Detect the presence of Redis Sentinels and turn off async and disallow HPA from being used.
Add an info message to the status of the APIManager CR to inform users that "HPA is currently not supported with Redis Sentinels"