MB-10179: Enable Delete/flush destination buckets xdcr tests

Change-Id: I110683a2d39e9447db672949b930cf90fb86d217
Reviewed-on: http://review.couchbase.org/39655
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>