shut down cbq-engine if cbauth initialization fails

In the existing codebase, the query engine keeps going if its attempt to initialize the cbauth client fails. We observed a case in a customer deployment where the system brought up the query engine before the cbauth server was ready, which meant the cbauth client never got correctly started up, meaning that access to password-protected buckets wasn't possible from the query engine.

The desired behavior here is that the query engine will shut down if cbauth client initialization fails. The babysitter can then bring up the query engine again a bit later, and hopefully the cbauth server will be ready at that time.