MB-23574 - add unit test for iterator single
MB-23574 - add unit test for iterator single

When run on commit (0fc17b1791), which is one commit before the fix
for MB-23567 (commit 86fdd130), the test introduced here fails.  On
the latest master, the test passes.

Change-Id: I96f23f82489798b2e270b1c9e120b5cf846ad926
Reviewed-on: http://review.couchbase.org/75935
Reviewed-by: Marty Schoch <ba9951d7d66412e2a57aea395f01176a793cf5eb@gmail.com>
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

steveyen/moss,couchbaselabs/moss,steveyen/moss