GOCBC-290: Errors not propagated from auth credential providers.
GOCBC-290: Errors not propagated from auth credential providers.

Motivation
----------
A bug within the authentication credentials provider causes
errors thrown by the provider to be ignored and authentication
to be skipped without throwing away the connection.  This causes
the connection to generate NO_ACCESS errors non-stop until the
connection is recycled.

Changes
-------
Changed the error passing code to correctly propagate any errors
generated by the underlying authentication credentials provider.

Change-Id: I45bd6dc8ec45246f43ca4b8b76a5b73214a9529d
Reviewed-on: http://review.couchbase.org/92851
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

brett19/gocbcore