CBQE-0:: Remove overkill dgm cases in failover tests

Change-Id: I5e11f4c2add4161a9b5eec54538d9b8c86f2fb3b
Reviewed-on: http://review.couchbase.org/41213
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>