Pass correct hostname for Admin to get AuthError

If the cluster was not 'localhost', a ConnectError was thrown instead

Change-Id: I577fd01a1708baa431803b004222f192d7cd5d37
Reviewed-on: http://review.couchbase.org/26627
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>