MB-8909 make errors for bucket password beautyful

without hardcoding width in html

Change-Id: I14a72cdd9d06a1edd3fbc4d4de53cd5f6e2fb4bb
Reviewed-on: http://review.couchbase.org/28541
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>