Adding new methods to DB API v2 (load_xxx and create_or_update_xxx)

* Methods load_xxx() which can return None unlike get_xxx()
* Methods create_or_update_xxx()
* Unit tests for new methods
* Refactoring DB tests

Change-Id: Ieb1985d0a9cf70b41a166a4f97251dd5c108576c
Merge "Adding new methods to DB API v2 (load_xxx and create_or_update_xxx)"