CBQE-0: decrease num of items for AutoFailoverTests.test_invalid_timeouts

Change-Id: I101329d785e926bc4c470f3f5e198ce139de1481
Reviewed-on: http://review.couchbase.org/26187
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>