MB-8909: make errors for bucket password visible

Change-Id: Ie5d476ff96c7c3e403d72884ab888f5004e6372f
[alk@tut.by: prettified error message look a bit]
Signed-off-by: Aliaksey Kandratsenka <alk@tut.by>
Reviewed-on: http://review.couchbase.org/28526
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>