CBQE-1069: less then 1M items per bucket for upgr tests

Change-Id: I765847293ac434d2b35b669a5bb6c6aaade22152
Reviewed-on: http://review.couchbase.org/24962
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>