MB-100: increase verification time for xdcr with reb

Change-Id: I67b73467ea8ec28a2448085d6dad880597ad1f6d
Reviewed-on: http://review.couchbase.org/24865
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>