CBQE-1531: add failover+ server failure test

Change-Id: Ia2b7698ff14d41117d325fcee223b24a82aeabb0
Reviewed-on: http://review.couchbase.org/29376
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>