CBQE-159: test_expired_keys_tap failed

Change-Id: I265a3d463ac3b650fa0b7b56e9a90a6f4b0a7d87
Reviewed-on: http://review.couchbase.org/22946
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>