MB-7171 made sure that Sample Buckets tab is hidden in mixed mode

.. and added code that prevents blinking of tabs during the reload
of the screen

Change-Id: I5a622bd4e1c91eb2ec75ff0b6cd6de076eff5da6
Reviewed-on: http://review.couchbase.org/27525
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>