MB-100:visualize-rebalance.rb: handle 2 checkpoint waitings/vb

We now note both waitings and in order to correctly match starts and
ends we now have additional condition for end to be after start.

Change-Id: I70bcb4c12a7339a7bcd5f4a8256d4a975324518a
Reviewed-on: http://review.couchbase.org/26070
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>