CBQE-0: use self.sleep instead of time.sleep for some tests

Change-Id: Id26ca5511dcce9e0de56e19451e9633c9d43e117
Reviewed-on: http://review.couchbase.org/31546
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>