MB-10721 don't use bucket auth for ui issued xhr's

UI doesn't use bucket auth, but the existence of the bucket without
password can allow the access to some url's even with expired token
which we want to prevent

Change-Id: I16d7635b3509a1da275272adad4289454710d4c5
Reviewed-on: http://review.couchbase.org/36121
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>