MB-20493 cbdatasource: refresh cluster on memcached auth error
MB-20493 cbdatasource: refresh cluster on memcached auth error

Found in a test case, during a swap rebalance, a cbdatasource worker
would continue to try to talk to a node that was swap-rebalanced out,
receiving an authentication error from cbauth.  This change propagates
that as an asynchronous refresh cluster kick event, which forces a new
cluster map to be retrieved, which will then shut down that worker.

Change-Id: I9ed21a8ae2ef2a628d5fe5edbbfe266ca0768513
Reviewed-on: http://review.couchbase.org/71197
Reviewed-by: Marty Schoch <ba9951d7d66412e2a57aea395f01176a793cf5eb@gmail.com>
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

couchbase/go-couchbase