Refactor add stream test cases

Change-Id: I8f9e14c252d7c00fe4f654448bd706262120df0b
Reviewed-on: http://review.couchbase.org/31076
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>