[AUR-3018] Implements joins using CouchDB in Datastore

- Added guard against test data not having the "data" property.

Change-Id: Ia537a7715f2b36737d20583623ed24a1fb515c5d
[AUR-3018] Joins in CouchDB

- Revised retun values when a document is inserted without it being in the test data (now it returns id and rev)

Change-Id: Idfcf9050ff8be1144f38597308c107a47e8961a8