CBQE-2131: basic tests for graceful failover

Change-Id: I73659eddfd7b3123998766b42743da81517722e4
Reviewed-on: http://review.couchbase.org/34640
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>