MB-100 wait_for_nodes timeout limits entire waiting.

Not the interval between changes. Because it's less confusing.

Change-Id: I1c79c6754e73a4901e7e7b226421105b80c80a15
Reviewed-on: http://review.couchbase.org/28870
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>