Fix to the rollback unit test failure.

When the rollback is performed on a replica vbucket, we should
wait until it is completed before getting a stream request again.

Change-Id: I42f2c1dbba31fc5aea820128d181b8ec1a553553
Reviewed-on: http://review.couchbase.org/33316
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>