MB-10721 limit the UI to ro_admin or admin access to /pools/default

... so if under any circumstances (like clearing cookies in browser)
UI will try to access this url without any auth it will for sure
get 401

Change-Id: I1dbd57824574b86bbc89b41d92aa463f52cf1585
Reviewed-on: http://review.couchbase.org/35926
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>