Add batch unit test

:Release Notes:
Add testing of batch, when in batch we have put and merge operation

:Detailed Notes:
Test batch with put/merge of the same object

:Testing Performed:
Compiled and tested localy.

:QA Notes:

:Issues Addressed:
[BHV-13271] DB8 don't response for batch reques

Open-webOS-DCO-1.0-Signed-off-by: Maksym Sditanov <maxim.sditanov@lge.com>

Change-Id: I04613ab696283e46c4707b4534c4b7a44a7ec000
Reviewed-on: https://g2g.lgsvl.com/6476
Reviewed-by: DCO Verification
Tested-by: Maksym Sditanov <maxim.sditanov@lge.com>
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>

Conflicts:
	test/db-core/CMakeLists.txt