CBQE-0: added sleep for expiration time in XDCR tests

Change-Id: If495ed58f08813209163c978fb5865cd0fb599b4
Reviewed-on: http://review.couchbase.org/33737
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>