MB-100: don't crash UI when /pools auth doesn't work

Logout does not remove auth cookie. That causes /pools request right
after logout to fail with 401. But despite that
UpdatesNotificationsSection still tries to render prettified version
which doesn't exist yet.

Change-Id: I1a49f55947b010f58101de09fbbc300a7f0ff930
Reviewed-on: http://review.couchbase.org/28020
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>