CBQE-1324: minor fix in AutoFailoverBaseTest.wait_for_failover_or_assert

Change-Id: I40e6e8d77fa13344e27ddb693ddb84ac5239ef28
Reviewed-on: http://review.couchbase.org/26674
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>